Never realized this, pretty interesting article from How To Geek:
Stamped pits vs organic dyes: Why commercial CDs outlived your CD-R backups
https://www.howtogeek.com/the-hidden-reason-why-your-cd-backups-are-slowly-dying/
"..... You might be wondering why burned CDs and DVDs are at any risk of data loss whatsoever. After all, lots of us still have our old albums from decades ago, and they usually work fine. But there's a difference between a pressed CD (the kind you bought in a store) and a CD-R or DVD-R. A pressed CD has pits physically stamped into the disc. Meanwhile, CD-Rs and DVD-Rs work differently. Your CD burner (something most people no longer even have at home) uses a laser to alter a recording dye layer to represent data, and that layer can degrade with age. The same goes for the thin reflective layer on your CD.
As that dye and reflective layer change, the disc eventually starts producing more and more read errors. ...... People call this "disc rot." But for recordable discs, it usually means dye breakdown and reflective-layer degradation that lead to more and more read errors over time. .... You might have two CDs burned around the same time period, and one of them will be just fine, while the other will be a lost cause. Why is that? ...... Different discs use different dye formulations and reflective layers, and certain combinations may be sturdier than others. Manufacturing quality is a factor, too. ..... How you store and handle the CD matters, too. Heat, humidity, and UV exposure can be deadly for optical discs. Physical wear, such as drops and scratches, are obviously not great either. ......"
https://www.howtogeek.com/the-hidden-reason-why-your-cd-backups-are-slowly-dying/