BERYL A. HOWELL, United States District Judge
The plaintiff Steven Tindal brings this action against the defendant Secretary of the Army pursuant to the Administrative Procedure Act (“APA”), 5 U.S.C. §§ 500, et seq., seeking to set aside the decision of the Army Board for Correction of Military Records (“the Board” or “the ABCMR”), which denied the plaintiff’s request to be reinstated to Reserve active status, promoted to the rank of Lieutenant Colonel, and transferred to the Oregon Army National Guard. The plaintiff served in an active-duty capacity in the United States Army for over twenty years. Following his retirement in September 2002, he twice appealed to the Board, claiming that he had filed a request to extend his active-duty service and thus that his retirement was an injustice that required correction. The Board denied his appeals, and the plaintiff now seeks to overturn the Board’s most recent denial as arbitrary and capricious and unsupported by substantial evidence. Both parties have filed motions for summary judgment, and the plaintiff has also filed a motion to supplement the administrative record with further evidence.
Since this is an administrative law case, the Court will first discuss the regulatory framework underlying the agency’s decision before discussing the facts and the procedural history.
A. Regulatory Framework
This case implicates a somewhat labyrinthine collection of United States Army personnel regulations governing how soldiers are administratively processed, particularly when they reach a certain maximum level of service. As discussed more fully below, the plaintiff was at all times relevant to this lawsuit a member of the Army Active Guard Reserve (“AGR”), and so the Court will discuss the Army’s personnel regulations as they apply to participants in the AGR program.
Under Army regulations, “[a]ll AGR officer personnel will be released from [active duty] or [full-time National Guard duty] when they have attained 20 years and 1 month of qualifying service for retirement purposes . . . unless they have been approved for voluntary retention under [Army Regulation] 600-8-24.” Army Reg. 135-18 ¶ 4-12 (1996). If a soldier wants to request an extension of his active-duty service, known as “selective retention, ” such a request “will be submitted when the soldier completes 19 years of such service” and “will be sent through command channels.” See Id . The “command channels” through which such requests must be sent depends upon whether the AGR soldier is serving in a federal or state chain of command. See Id . For an AGR soldier serving in the Army National Guard (i.e., the state chain of command), the requests would be sent to the National Guard Bureau (“NGB”). See id.
Retirement from the AGR based upon maximum years of service can be either voluntary or involuntary. “A mandatory retirement is required by law and is initiated by [the Headquarters of the Department of the Army].” Army Reg. 600-8-24 ¶ 6-24a (2002). On the other hand, “a voluntary nonwaiver retirement” may be requested by an officer, and “it is Army policy to approve a voluntary nonwaiver retirement application when an officer will have served at least 20 years of active Federal service as of the requested retirement date.” Id. ¶ 6-14a; see also Id . ¶ 6-20 (outlining steps for processing a voluntary retirement application). Hence, voluntary retirement in the AGR program is initiated by the soldier who applies for such retirement, and involuntary retirement is initiated by Army Headquarters and proceeds by operation of law. The timing of an AGR soldier’s retirement, however, is not necessarily correlated to whether the retirement was voluntary or involuntary because “[a]n officer may request retirement and be retired voluntarily on his or her mandatory retirement date.” See Id . ¶ 6-24a; see also Id . ¶ 2-23d (“The officer’s separation will not be delayed past the scheduled release date due to nonsubmission or late submission of a voluntary retirement request.”).
Related to both retirement and selective retention, a soldier is required to meet certain minimum medical and fitness criteria. For example, in order for a soldier to be retained and “selected for subsequent duty in the AGR Program, ” he “must possess” certain minimum qualifications, including certain “Physical and Medical” qualifications. See Army Reg. 135-18 ¶ 2-4b & tbl. 2-4; see also Army Reg. 40-501 ch. 3 (2002) (laying out “Medical Fitness Standards for Retention and Separation, Including Retirement”). These qualifications include “body composition/weight control standard[s]” and “medical fitness standards.” Army Reg. 135-18 tbl. 2-4. Generally, medical evaluation of whether active-duty soldiers meet minimum physical requirements is only initiated “when a question arises as to the Soldier’s ability to perform the duties of his or her office, grade, rank, or rating because of physical disability” or a soldier’s commanding officer “believes that a Soldier of their command is unable to perform the duties of their office, grade, rank, or rating because of a physical disability.” See Army Reg. 635-40 ¶¶ 4-6, 4-8 (1990).
As to retirement, “[m]edical examination prior to retirement is required, ” and “will be scheduled not earlier than 4 months prior to the retirement date.” Army Reg. 600-8-24 ¶ 6-6. “When a soldier is being processed for separation or retirement for reasons other than physical disability, ” however, “continued performance of assigned duty commensurate with his or her rank or grade until the solder is scheduled for separation or retirement, creates a presumption that the soldier is fit.” Army Reg. 635-40 ¶ 3-2(b)(2). This presumption may be overcome if, inter alia, “[a]n acute, grave illness or injury or other significant deterioration of the soldier’s physical condition occurred immediately prior to, or coincident with processing for separation or retirement for reasons other than physical disability and which rendered the soldier unfit for further duty.” Id. ¶ 3-2b(2)(b).
In addition to these general medical and fitness requirements, there are two Army administrative systems relevant to this case, which are designed to evaluate soldiers’ fitness for duty. The first is called the Physical Performance Evaluation System (“PPES”), which is “designed to evaluate soldiers who have been issued a permanent physical profile with a numerical designator of 3 or 4 . . . to determine if they have the physical ability to satisfactorily perform their primary military occupational specialty (PMOS) . . . worldwide and in a field environment.” See Army Reg. 600-60 ¶ 2-1. The PPES establishes an “administrative screening board” called the Military Occupational Specialty/Medical Retention Board (“MMRB”) to make this determination. Id. Referral to an MMRB is required, inter alia, when a soldier is issued a permanent physical profile with a numerical designator of 3 or 4, see Id . ¶ 2-2, though referral to an MMRB is not per se required as a part of the selective retention process. A soldier is exempted from mandatory referral to an MMRB if he is “[a]n active duty officer who is within 1 year of [the] date of mandatory retirement for age or length of service” unless he has “sufficient time remaining to be eligible for reassignment and receive assignment instructions.” See Id . ¶ 2-3f. After evaluating a soldier, the MMRB may recommend either (1) retention of the soldier’s PMOS; (2) placing the solider in a probationary status; (3) reclassification of the soldier’s PMOS; or (3) referral of the soldier to the Army’s Physical Disability Evaluation System (“PDES”), see Id . ¶¶ 4-17 to 4-20, which is the second administrative system relevant to the instant case, discussed below. Any enlisted soldier “pending MMRB action and follow-on determinations may not re-enlist, ” though “[i]f otherwise qualified, they may extend their current enlistment” in accordance with Army regulations. See Id . ¶ 3-7a. If a soldier is “retained in [his current] PMOS, reclassified into another PMOS, or found fit by the PDES, re-enlistment or extension of enlistment will not be denied on medical grounds.” Id. ¶ 3-7c.
The PDES, much like the PPES, is concerned with “determining whether a Soldier is unfit because of physical disability to reasonably perform the duties of his or her office, grade, rank, or rating.” See Army Reg. 635-40 ¶ 1-1. Similar to the screening role played by the MMRB in the PPES process, a medical evaluation board (“MEB” or “MEBD”) is involved in the PDES process. See Id . ¶ 2-10a. “MEBD’s are convened to document a soldier’s medical status and duty limitations insofar as duty is affected by the soldier’s status, ” id. ¶ 4-10, and a soldier is generally referred to an MEBD, like an MMRB, when a question arises about the soldier’s ability “to perform the duties of his or her office, grade, rank, or rating because of physical disability, ” see Id . ¶¶ 4-6, 4-8. A soldier may also be referred to an MEBD by the MMRB,  see Army Reg. 600-60 ¶ 4-20, and referral to an MEBD is required if a soldier has certain medical conditions, including diabetes mellitus, “when proven to require insulin or oral medications for control.” See Army Reg. 40-501 ¶ 3-11d.
B. Factual and Procedural Background
In March 1976, the plaintiff enlisted in the U.S. Army. See Admin. R. (“A.R.”) at 269– 70, ECF No. 15-6. After completing just over three years of active service, the plaintiff was honorably discharged on February 29, 1980. See Id . at 267; see also Def.’s Statement of Facts (“Def.’s Facts”) ¶ 2, ECF No. 16-2. In December 1982, the plaintiff was appointed as a Second Lieutenant in the South Carolina Army National Guard. See A.R. at 6, 251–52. The plaintiff was promoted to the rank of First Lieutenant in December 1985, see Id . at 226, and to the rank of Captain in November 1988, see Id . at 6, 207. On September 30, 1993, the plaintiff was transferred to the Oregon National Guard, see Id . at 193–97, and in October 1994, the plaintiff was first ordered to active duty in the AGR program, see Id . at 6, 185–86. In February 1997 the plaintiff was promoted to the rank of Major. See Id . at 6, 168. Also, in November 1997, the plaintiff was diagnosed with diabetes mellitus, which he “controlled . . . with exercise, diet, and limited oral medication.” See Am. Compl. ¶ 5, ECF No. 13; A.R. at 122. The plaintiff was subsequently issued a “‘3-P’ permanent profile” in 1998 as a result of his diabetes diagnosis, though he “was not referred to an MMRB” at that time. See Am. Compl. ¶¶ 6, 9.
In December 2001, the plaintiff was notified that he would be released from active duty and transferred to the Retired Reserve on August 31, 2002, after having accrued twenty years of active federal service. See Def.’s Facts ¶ 11. At some unspecified time in 2002, the plaintiff submitted a request for voluntary retirement. See Id . ¶ 12; A.R. at 6. The plaintiff claims that in or about February 2002, he requested selective retention in the AGR program. See Am. Compl. ¶ 21. Also at some point in 2002, the plaintiff was processed through either an MMRB or an MEBD, though it is unclear from the record when or how the medical referral was initiated and what the outcome of the medical referral was. See A.R. at 12; Pl.’s Opposing Statement of Facts (“Pl.’s Facts”) ¶ 11-B, ECF No. 22-2; Am. Compl. ¶ 19. The plaintiff alleges in his Amended Complaint that he was referred to an MMRB in June 2002, and that his “MMRB later unfavorably referred him to a follow-on MEB as not deployable and for further disability processing.” See Am. Compl. ¶¶ 31, 33. On July 23, 2002, the plaintiff was once again notified that, pursuant to his application for voluntary retirement, he would be retired from active duty and transferred to the Retired Reserve, effective August 31, 2002. See A.R. at 145. In accordance with this notice, the plaintiff was in fact released from active duty on August 31, 2002, after serving twenty years, one month, and twenty-four days of active federal service. See Id . at 125, 145.
The plaintiff’s personnel record reflects a long and distinguished career in military service. On October 20, 2002, the plaintiff received the Meritorious Service Medal for his twenty years of “exemplary service coupled with his superb technical expertise.” See A.R. at 138. His commanding officers also consistently and enthusiastically recommended him for promotion to the rank of Lieutenant Colonel. See Id . at 140–41 (“Promote when eligible.”); id. at 147 (“Promote to lieutenant colonel and give him every opportunity for our best professional development schools.”); id. at 153 (“MAJ Tindal is Battalion command material and should be considered when eligible.”). On September 4, 2002, a promotion board selected the plaintiff for promotion to the rank of Lieutenant Colonel, but the promotion selection was declared null and void due to the plaintiff’s transfer to the Retired Reserve prior to the approval date of his promotion. See Def.’s Facts ¶ 16; A.R. at 118, 134.
On September 9, 2005, the plaintiff submitted an application to the Board,  requesting reinstatement to active duty in the AGR program, promotion to the rank of Lieutenant Colonel, and transfer to the Oregon Army National Guard. See Def.’s Facts ¶ 17; A.R. at 120–23. In his original application, filed pro se, the plaintiff contended that he had “been unjustly treated compared to [his] Active Component counterparts” because “the National Guard requirements and policies are more restrictive than the Active Component.” See A.R. at 122. Specifically, the plaintiff contended, “if I had been a Regular Army officer, I would have been able to serve 24 years at my rank, ” but “because I was a member of the Army National Guard and not the Regular Army, I was not given the opportunity to continue my career and retire as a Lieutenant Colonel or possibly a higher rank.” Id. at 121. The plaintiff also mentioned in his submission to the Board that “[t]he Oregon National Guard tried to extend me before my retirement date; however, the time ran out to my retirement date without any positive results.” Id. at 122. Further, the plaintiff stated that the NGB had “directed that [he] go through a Medical Evaluation Board, ” and that although “Mr. Grant Moyer, the Medical Evaluation Board director . . . stated [he] would not have to go through an MRB to stay on Active Duty, ” he nevertheless “had to go before an MRB.” Id. In short, the plaintiff argued in his original appeal to the Board that he had been treated unfairly because he was forced to retire after twenty years of active service, while officers in the regular Army component could serve in active duty in the rank of Major for up to twenty-four years. On August 31, 2006, the Board considered the plaintiff’s arguments and evidence, including his Board application and his military personnel records, and the Board denied his request for relief. See Id . at 115–18.
On February 26, 2010, the plaintiff filed his original Complaint in the instant action. In his Complaint, the plaintiff presented a different version of the arguments he advanced before the Board. In particular, the plaintiff alleged that “[h]e attempted to argue that while his [active federal service] extension was pending, NGB directed that he go through a useless Medical Evaluation Board and MRB to determine if he was physically fit to continue with his career.” See Compl. ¶ 35, ECF No. 1. The Complaint further alleged that the plaintiff “was referred to an MEB for diabetes, but that condition was never an issue that affected his performance.” Id. In this regard, the plaintiff alleged that “the [NGB] in May 2002 directed Major Tindal be processed for disability retirement through a MEB and MMRB, both at Fort Jackson S.C.” Id. ¶ 27. The plaintiff complained that “[t]he Board did not address the MEB or MMRB issues, nor the injustice of NGB insisting on these boards until the clock ran out on Tindal’s extension request.” Id. ¶ 36. Although conceding that “it was not explicitly clear ...