If you need to recover data from a defective or damaged optical disc, I would recommend using this program
https://www.videohelp.com/software/IsoPuzzle (Currently at 1.7Beta)
Originally posted here by the Author but the links are dead but maybe useful for info
What is nice about this program is that it creates an ISO which you can add to or come back to later. The benefit of this means you can merge data from multiple disks and use multiple drives on the same disc.
I had two CD's of an old program which were both very defective and after several passes only came up at 30% and 3%. I was able to recover 99.9% plus and only had 3 missing pieces after trying for three days doing various things. Note these disc didn't look like professional mass produced ones (greenish goldly silver dye) and more like ones burned on a desktop writer. They were not particularly badly scratched and I suspect the dye had gone bad'ish.
Typically after doing lots of different things and getting down the just 5 missing pieces my colleague found an additional three discs in folders, but yay I managed to get all the missing pieces. Note that in this case the last two sectors were never recovered even with trying all discs but it didn't seem to matter and I suspect they were not data sectors.
The drives I am using are a TSSTcorp USB one which is a CD/DVD RW (this works the best) and an Apple super drive HL-DT GX40N (both work well with the greenish goldly silver dye discs), and an internal (laptop size ) PLDS DVDRW which barely reads them. These drives all use one laser and I wonder if using an old CD only drive would have helped.
Trying all the discs you have of the same type after several passes rather than exhaustively checking them one by one will help speed up the process as it will pick up more data and therefore you will need less time to find the missing data.
Lesson learned? back up the same data to at least three discs for archiving so you can use them all to reconstruct it.