Irrelevant old guy anecdote alert: I borrowed my dad’s green M65 he brought back from Viet Nam a few times in the 1980s, as a teen. The liner was newer - a fleecy thing that made it very warm. They were never issued in the Australian army but some units would turn a blind eye to privately purchased kit in the field, as long as it didn’t look out of place. In the mid 1990s I bought an M65 in regulation DPCU camo made in Hong Kong and had a local tailor make-up a wool liner for it. Never got to wear it because I was sent to a unit that enforced uniform standards very strictly before the next Winter.