In the three examples I gave as being interested in, PSA gives specific info on their bolt carrier group in each rifle. The m-lok example says it's bolt is 9130, the classic says it's non-logoed Toolcraft Carpernter 158 mil-spec and the moe says it's mil-spec Carpenter 158.
It appears to me they are fairly clear in their descriptions of the individual bolts of each package and it's up to the buyer to pay attention to what your buying and to talk with them to clarify any issues. This is also the reason I've brought up this topic on this forum. I have not kept up with ARs and your advice is already proving helpful.
