How to reread very dirty CDs?

I have heard about ; when I feed it with a very dirty CD, it hardly read it; but when I give it a copy of the same dirty CD made with alcohol120, it reads it 10 faster; technically, how can that happen ? is it passible by software to detect the reflectivity of a disk ?

If you have the fast error skip option enabled, what ever Alcohol cannot read, it just skips.