Peter, although seeing lots of Grande when I go to pizzeria suppliers tells me that quite a few pizzerias are using it, I think the vast majority are using typical cheap food service mozzarella, which on the retail level, would be comparable to private label.
It may be not be the same for different parts of the country, but, when I was attending college in Illinois, I'm practically positive the supermarket had their own brand of mozzarella- and that was pretty much in the middle of no where. Does your local supermarket put out their own brand of cheese?
And, although I feel a lot stronger about other deviations from the style, I don't think provolone quite fits the definition of NY pizza. I'm not saying provolone is bad, but I think it deserves it's own classification. If I had my way, though, a LOT of approaches would get their own style. Imo, the current umbrella for NY style is way too big. NY style deserves to be defined just as rigidly as Neapolitan. But that's another conversation