I bought a Spike's AR 15 from a small dealer in my city. At least I thought it was all Spike's. I have looked at all parts and it looks like I got an ST upper and lower but there are no ST stamps on anything else. I removed the hand guard to look for barrel marks and there was no indication at all as to the length, twist or composition. The bcg had no marks (probably just some mil-spec part). Anyway, I was installing a single point sling mount and thought I would have a rear detent spring pop out but didn't see it. When I looked at the hole for the spring it had already been tapped and a screw put in.

My question is, does ST do this as a matter of course or did someone else do this? This AR does look new.

If your lower's serial number starts with SAR, then the rear detent should be tapped and screwed.

As for the other parts, if you can take pics and link to them I can tell you if they are ST or not. The lack of ST logo on the BCG is quite suspect.