My brother was an engineer at the Sony CD plant. I got a tour from him back in the early 90s. Fascinating. He told me CDs have a min design life of 15 years. They are not considered archival. The polycarbonate discs have the pits molded in them. That’s the music information. The next step is sputtering a layer of Aluminum just a few atoms thick onto the disc. A clear coating is added to protect the Aluminum and the label printed on. I could imagine that a disc could be restored if the Aluminum coating could be removed without damaging the surface of the polycarbonate disc and reapplying the Aluminum coating. It would have to be a very valuable disc to go to all that trouble.
Just for fun that day, I brought home an uncoated disc. It was simply a clear CD with the pits molded into it. I tried it in my CD player. It would not play. No surprise, just curious.