Lots of old CDs had that problem - called "bronzing" because the reflective aluminium layer oxidises when the ink eats through the lacquer layer or the lacquer fails at the edges - I had half-a-dozen from Unicorn-Kanchana and Hyperion which needed replacing, pressed by Philips-DuPont in the UK. In that case I was given free replacements for all of them, and the rest of my discs seem OK.