With 2 coatings it took off the lighter parts of a paint rub (white on my santorin blue), but the darkest part still remains. Perhaps 3 or 4 more tries would fix it?

I have some light scratches that are not down to the metal, but IHG isn't helping with blending them in. What should I try now?

scratch remover. Keep in mind that I've got some rubs and odd marks that just simply won't come out. I'm a little hesitant to move up to a true rubbing compound, just because brilliant black is a very fragile paint, so I'm thinking I'll just have the car professionally buffed sometime.