You're half right for the wrong reasons. Disc rot just doesn't happen to stamped original discs, only writable discs rot. Old cheap discs might degrade for other reasons of course (like scratches or labels delaminating and tearing away at a substandard construction), but the data layer of original stamped discs doesn't decompose because it's mechanically stamped into the data layer. Original discs would have been stamped foil pressed between two layers of plastic. Cheap discs sometimes just skipped the top layer of plastic so that the data layer was just under the painted label. Writable discs especially using this cost saving technique. Thus any damage to the top label would damage the data layer. Writable discs rot because the bits are burned into a different kind of data layer film that can fade or otherwise decompose, but I doubt you'd be able to actually see dots from rot. Using the wrong kind of pen or using sticker labels could easily damage the data layer. If you hold a disc up to a light source and see dots of light through it, the foil layer has been scratched and it will be unplayable, but this is physical damage not rot.