I believe that eight years is correct that they have that long. What happened? Could it be that his number to Vietnam did not come up after that? Not everyone went to Vietnam. My father did join the Air Force at 18 until 22 and he went to Oklahoma and Nebraska for his duties...lol. No Vietnam for him. I can’t answer those questions as there are no answers that I can give that would be accurate.
You said...he didn't go in the military because of his mission responsibility. When that isn't actually accurate...As he "could" have done both. He didn't.
fwiw-