Unfortunately as a SEGA Saturn collector, this is no surprise, and disc rot has taken claim to games that could otherwise be worth hundreds of dollars today. :(
Weirdly, almost all of even my much older audio CD’s - stored in the same bin away from heat and moisture - don’t have this issue.
I have to wonder what effect the specifics of the manufacturing process have on how likely a disc is to experience disc rot, as actually even within the SEGA community it’s widely accepted that Saturn discs have an unusually high rate of failure compared to other compact disc collectables.
However - importantly - my original point about quality also applies to backups of these mediums as well - so, assuming any copy of that audio CD has been properly archived and backed up, it will pretty much always be the best quality it can possibly be. Backing up a DVD these days - when there is a majority of the time a superior Blu-Ray or streaming release, is frankly pretty pointless, except for, unusually - the much more abundant amount of special features often found on DVD’s.
I never understood why special features pretty much went the way of the Dodo when Blu-Ray became the standard.