Like also for floppy disks, the older CDs had typically a higher manufacturing quality than the more recent.
This is shown in the table from the parent article, where there are 3 rows for CD-R, the best, which were specified as suitable for archival purposes, but Kodak and the few other manufacturers of such CD-R have stopped soon their production, the second best, which were the original CD-R with phthalocyanine dye and then the other CD-R, whose expected lifetime is only half, with cheaper dyes, which were introduced on the market later.
Also, as expected, the table shows that the higher the information density is, the lower the expected lifetime is, when similar materials are used.
I think that optical disks is a lot like a Lemons market[1]. Buyers can't evaluate the quality (durability) of disks, so are not willing to pay high prices, which drives high quality suppliers out of the market, which causes buyers to offer even less, which drives even more quality suppliers out of the market, resulting in a death spiral.
Do you test the data is identical? I've got a stack of old CD-R's containing mp3 files from 20 years ago and lots have unreadable files or worse: data that reads correctly but won't play without glitches. (corrupt mp3's can produce loud spikes that are very bad for your ears and/or audio equipment)
