I had some badly made discs in a 50 pack that I bought a while back. Have you physically looked at the discs to see if there are any defects? Its kind of funny that one 50 pack had approx. 5-10 discs with defects and the other 50 pack I got for "free" had no defects. Some of the defective discs had a "line" that was visible from the top face, I'd say it was a crack or break in the aluminum layer. The remainder had poorly lacquered tops that easily chipped through and chipped off the ally layer (EDIT: I noticed the problem because they all had chips in the lacquer to start with and when I tried to enlarge the chips, they enlarged quite readily). The remaining discs in the 50 pack have like a piece of dust in approx. the same place on the lacquer side, but are otherwise not noticeably defective. I have a couple of the "dust" discs burnt and they had Kprobe readings equal to any TY that I've used and work fine in my car's CD player, so far. I didn't complain to Ritek over the 5-10 discs that were defective because at $20 for 100 discs (2-50 packs, buy one get one free), I still made out pretty good, IMHO.
I did burn one of the discs I found with a "line" in the ally layer (I think that's where it was because it was more noticeable on the top side vs. the underside), it was not the one with the most pronounced line, but it did give pretty bad Kprobe results.