Mold frequently grows on the luminous paint, but not typically on the dial surface. I am curious how you have concluded that the damage to the surface of the dial is mold, as opposed to the many other types of damage that are often seen on dial surfaces (e.g. degradation of the lacquer layer, the paint, etc). Or perhaps you are referring just to the lume?
I will just say that, in general, I would not buy a watch with the idea that the dial can be greatly improved. On occasions, I have seen a dial cleaned successfully, but it is risky and attempts to improve a dial often cause more damage. Moldy lume sometimes stabilizes, but more often gradually darkens further over the years.