I think most of us agreed that these sunroofs were "port of entry" installed. In other words, ARI (Alfa Romeo, Inc.) took cars off the docks to have sunroofs installed.This is a point of a fair amount of discussion, whether there was such a thing as a factory sunroof on GTVs or Berlinas. The view I agree with is that there weren't any, and they were all done by distributors, dealers, or aftermarket installers, some to such a high standard that they look like factory work.
Not saying yours isn't, but the researchers I trust convinced me the factory never did any. And there's nothing in any factory parts book or owner's manual about it that I've ever seen.