Cros-Interleaved Reed-Solomon Code (CIRC) allows to recover data from up to about 4mm scratches along the track. Between 4-8mm data is interpolated while scratches longer than 8mm cause dropouts - at least for the most of CDPs working in real time (being not able to read sector multiple times). Ripping programs can go over sector multiple times until they obtain proper checksum. I had MAX (OSX) set to "Do not allow to skip" making program going forever with unreadable CD. I had few CDs that I was able to recover that way after couple of hours of ripping. Now I use XLD set to "Max Retry = 200".
I had CDP refusing to play because of dirty lens, then because it needed a little bit of grease to finally stop reading because of worn felt on the magnetic ring that supposed to hold CD down, allowing it to wobble. I had some original CDs with defect - visible wave in internal foil, as well as few CDRs with the same problem. The best CDRs I’ve ever used were Taiyo Yuden. Now I only use HD (server) with a couple of backups.
I had CDP refusing to play because of dirty lens, then because it needed a little bit of grease to finally stop reading because of worn felt on the magnetic ring that supposed to hold CD down, allowing it to wobble. I had some original CDs with defect - visible wave in internal foil, as well as few CDRs with the same problem. The best CDRs I’ve ever used were Taiyo Yuden. Now I only use HD (server) with a couple of backups.