This is also why you can buff scratches out of the bottom of damaged CDs with a repair kit and possibly restore them. The coating on the bottom is fairly thick. Damage to the less protected top isn't noticed immediately, but is potentially more dangerous if you actually expose the material inside. Most CD-R blanks are very vulnerable to damage on the top. I find that putting an adhesive label on the top of each disc I make not only lets me see what I've got on it, it gives me a bit more piece of mind that I've added more protection to the sensitive top.
Some warnings are in order.
There is some potential that improperly centered labels will throw off the weight of the disc so that it spins oddly. I like putting labels on anyway. I got a set from Neato . I'd rather pay the extra money for a label design that seems thoroughly tested, as the money for the labeling is cheap compared with the potential damage if I got something that screwed up my discs. The included software works, but it's not very impressive.