Sabog was born in Hawaii. He enlisted in the Army in 1945, and his last assignment was as a logistics sergeant with the 507th Transportation Group at Binh Dinh, South Vietnam. When his hitch was up he was to travel to Fort Bragg, North Carolina to serve with the Headquarters Company, 12th Transportation Group. His whereabouts from February 1970, to February 1996 are not known with certainty. There is no record of his arrival back in the United States.
Due to an "administrative glitch" Sabog's loss was not noticed by the Army. His loss was only noticed when his family contacted the Army, in 1973. In 1974 he was listed as a deserter. At the time of his disappearance Sabog had served in the Army for 24 years - his entire adult life.
Sabog's brother wrote to President Jimmy Carter, protesting the listing of Sabog as a deserter. Subsequently a panel of Army and FBI investigators looked into his file and concluded it was very unlikely a soldier with a good record of 24 years of service, who was eligible for retirement, and was headed back to the United States would desert, when he could easily just retire, and his status was changed to Missing In Action.
By 1993, Vietnam had been cooperating with the USA, for years, to try to identify and repatriate remain of those listed as MIA, and remains believed to be Sabog's had been repatriated. In 1996 the Army was in the process of trying to confirm those were Sabog's remains when an elderly man applied for Veteran's Benefits, using Sabog's name and Army ID number.
Sabog could not give an account for the years since his disappearance. Authorities determined that he had lived in Rossville, Georgia, where he went by the name Bobby Fernandez, for the previous ten years, where he had been working as a live-in caregiver for an elderly woman. He had gone to the local Police in 1993, with a concern he was an AWOL GI, named Mateo Sabog, but the Police check with Washington suggested this wasn't possible as Army records showed Sabog was deceased.
Sabog's fingerprints matched those in his Army file. He was briefly re-enlisted, and sent to the Eisenhower Army Medical Center, Fort Gordon, Georgia, for a complete check-up, and then given an honorable discharge. After his discharge Sabog returned to Hawaii, where he lived on his Army pension, near his family, until his death in 2007.
- Bill Kirby (2019-05-26). "Missing and memorialized, a Vietnam veteran was found". Augusta Chronicle. https://www.augustachronicle.com/news/20190526/missing-and-memorialized-vietnam-veteran-was-found. Retrieved 2020-01-25. "Three years after his name was placed on the memorial, the frail 73-year-old sat in Fort Gordon’s Eisenhower Army Medical Center struggling to tell both the Army and his family what he had been doing the past 26 years."
- "SABOG, MATEO". Task Force Omega. http://www.taskforceomegainc.org/s248.html. Retrieved 2020-01-24.
- Bradley Graham (1996-03-09). "Missing Vietnam veteran resurfaces". Washington Post. Archived from the original on 2019-05-09. https://web.archive.org/web/20190509114819/https://www.washingtonpost.com/archive/politics/1996/03/09/missing-vietnam-veteran-resurfaces/e852026c-2c14-4638-98da-b4c5f354a32a/. Retrieved 2020-01-24. "'We're welcoming him back as a long lost soldier who has returned,' said Lt. Col. Bill Harkey, an Army spokesman. In fact, Army offices were abuzz yesterday with word of Sabog's remarkable reappearance, as more than one official remarked in interviews that the story had the makings of a made-for-TV movie."