Originally Posted by scoobiedoobie

There is some bad information being given here. Suggesting something such as 'a copy of a copy of a copy' will contain more and more errors is false. Copying a DVD is not analog, it's a digital format. If it copies it 1:1, it creates an EXACT copy, the data is identical. Do a proper backup without read errors and you can make 10,000 copies of a copy and the 10,000th copy will be identical to the original disc. Example: Successfully rip a DVD as an ISO image, all that you are retaining is the data on the disc, nothing else.

To the original topic, for whatever reason the discs are degrading. Could be poor handling or storage, poor media. Discs CAN and WILL degrade, whether they are pressed or burned media, and it goes without saying that poor quality media will have more issues with degrading.

Rip each of the discs using DVD Decrypter and make a backup of each disc onto good media. If DVD Decrypter gives you errors, increase the number of retries in DVD Decrypter or try ripping the discs with ISOBuster.