I will type this one more time...
[i]Most[/i] USGI mags are milsurp...
When I was in, we cleaned mags in bunches. Strip them down to piles of floorplates, springs, followers & bodies. Reassembled in reverse order.
When I buy mags, I assume the name on the floorplate is anything but the body manufacturer. Unless you buy a mag NIW, I would say you can assume the same.
I go for rivet count, lip & tab condition. Nothing more.