It doesn't give you any cores, hell, it doesn't even change your flag. Obviously, from a plausibility perspective, I can understand all these newly conquered territories not counting as cores, but surely there should be some bonus, aside from changing the name of Berlin. Hell, if restoring the Holy Roman Empire can create so many cores (actually, restoring the actual Roman Empire does even better), surely the GGR should, as well.
Also, shouldn't it be the Greater Germanic Reich?
Also, shouldn't it be the Greater Germanic Reich?