Rick, nobody said they were all good receivers. AAMOF any of them with a SN under 2000 was/should be highly suspect. According to CAI( I did some lengthy research on this five years back) they had a vendor making the receivers that was, shall we say, a little lackluster with their machining operations. They(CAI) admitted they threw away over 600 of this vendor's receivers themselves). The new vendor they got(Lithgow) ran a tight ship and QC was alot better. These are the in-spec receivers. Also, there was some overlap in the receivers between what they could use of the original vendor and Lithgow.
BTW, I scrapped out a few of them myself, they used really good parts-kits on the first 3000 they assembled. I was finding unissued Triggergroups, Op-Rods,Bolts and internals in them, most barrels...not so much.