I thought that CD-Rs would last forever, like CDs. I learned otherwise.
It really depends on the speed you burnt (the slowe the better at least back then) and the CD-R brand/type used. I had several – some realy the same cheaper brand – going bad as well over the years. They start to produce a scratchy sound towards the end mostly, especially if really 70+ minutes. But the very first CD-R I ever burned 25+ years ago still works. Last time I tried it at least. I have imported all CD-R to my hard drive already.