I have a CD with actual edge oxidation. It looks like a jagged brown edge around the disc working its way in. I only have one that suffers from that problem, thankfully. CDs are more sensitive to physical damage than, say, LDs or DVDs, however. DVDs and LDs have a plastic layer on both sides, but not CDs. CDs have a plastic layer on bottom, but on top there's just the material of the label and some sealant. If you get a scratch on the bottom of your CD, as long as it isn't too deep you can polish it out. Deep scratches might be fixable with a kind of filler. If you scratch the top of the CD, however, you are extremely likely to damage the data substrate, because there's so little protecting it from the top. I had to pass on a great deal on SamSho 4 on the Saturn because there was a small scratch on the top of the CD that clearly penetrated the data substrate.