You mean that saying Craig->Creg is wrong? It's always bothered me and it's very jarring, but if you grew up being called Creg, then it wouldn't be wrong. But it sounds so wrong to me.

I feel like it doesn't make sense, because then Greg should be spelled Graig, but that's the whole point, language evolves in an inconsistent way, and the only defining point of correct pronunciation is really "how do the majority of people say it", and that is often only a regional thing too.

Either way, the assertion that because something is a name it cannot evolve in pronunciation is easily disproved.