In the late 1990s, members of the Joint Task Force - Full Accounting confirmed to this anon in Saigon that some men were left behind alive after the war ended in 1975, and they knew it.
By 2001, some of them were dead in a 'mysterious' helicopter crash in the mountains of Vietnam.
https://www.cbsnews.com/news/mia-advance-team-dies-in-crash/