I think there were live Viet Nam era POWs still alive there in the mid-80s.
My dad served in Korea. He said very little to me about his experience there. But one thing he did say was that one of his big fears he and his friends had was being captured and being taken to the Soviet Union. He more or less said that it was known that some captured Americans were taken by train into the Soviet Union and never seen again.
No there weren’t. John McCain said so. /sarc