Got mine in Boise about six months ago. I looked at two, both had holster wear. I picked the one that looked the best internally even though it had more cosmetic slide wear. Not a thing wrong with its function. Never looked at this bunch but assume they also were carried a lot and fired a little. Are you saying the ones you saw were worn out?
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek