Is there a point to where you will no longer be able to remove oxidation from your gelcoat, and if there is, how do you know that you are at that point?

My boat has good color where one of the last owners had it's registration numbers (he had put it on the black in the middle, instead of the cream at the top of the hull) but the rest it fairly oxidized, marbly gray and black color instead of a glossy black. You can still see a good reflection after and normal coat of wax (carnuba w/teflon) though. You can also tell that he replaced the side decals as well because he was a little off with the placement of the new.