I appreciate the response. I think it's possible it could be early stages of that. It's mostly towards the center of the disc. Can rot account for wavy off colored lines circling the CD?
I don't think what you're describing is rot. I've noticed it before but just decided it's the way the light reflects off either the plastic, bonding or metal.
Is it perhaps iridescence? Rather pretty rainbow colours, doubtless caused by interference somewhere? I just looked at a disk I bought new today, and on the label side there's a set of fairly faint quasi-rings (like rings with epicycles), and on the clear side beautiful strong radial rainbows.
Ordinary pressed CD and DVD media are every-day examples of diffraction gratings and can be used to demonstrate the effect by reflecting sunlight off them onto a white wall. This is a side effect of their manufacture, as one surface of a CD has many small pits in the plastic, arranged in a spiral; that surface has a thin layer of metal applied to make the pits more visible. The structure of a DVD is optically similar, although it may have more than one pitted surface, and all pitted surfaces are inside the disc.In a standard pressed vinyl record when viewed from a low angle perpendicular to the grooves, a similar but less defined effect to that in a CD/DVD is seen. This is due to viewing angle (less than the critical angle of reflection of the black vinyl) and the path of the light being reflected due to this being changed by the grooves, leaving a rainbow relief pattern behind.