I believe a not insignificant amount of this gear originated (BAR's, M1carbines etc) came from China who in turn captured large amounts of western materiel during their civil war and following that, in the Korean war. I once had the chance to sift through a number of NVA/VC small arms that used to be left out for display/supervised handling, at the Vietnamese Airforce museum in Hanoi.
This was 23 years ago now, so memory might be a little fuzzy, but some of the M1 Carbines in particular, seemed to have typical Chinese small arms inspection markings on them, so perhaps signs of Chinese arsenal refurbishment.
As a side note of interest, displayed just down the road, outside the Airforce headquarters and still in good overall condition was the wreck of a substantially complete US Navy F4 Phantom, ejector seat rods still extended, this was recovered in complete (but somewhat crumpled) condition after being shot down in 67, both crew members being captured unfortunately after ejecting.
Back then it was in very good order, clearly having been undercover and being stripped of internal avionics, what a prize this must have been for the Eastern block back then!
When I was noticed reaching for my camera it went down like a lead balloon and I was forcefully, but polity, advised it would not be a good idea !
I believe this same wreck, now in poor condition has moved over the road to the Army museum.