I'm guessing that GP102 is actually a 3840 core part (50% bigger than GP104), but this initial release is being cut down to improve yields on the immature 16nm

I'm guessing that GP102 is actually a 3840 core part (50% bigger than GP104), but this initial release is being cut down to improve yields on the immature 16nm process. They did something similar with the original GK110 Titans - the first Titan had 2688 cores enabled, and a fully unlocked 2880 core Titan Black came later.