I seem to be missing something when the two bit scheme is introduced it's said that it's the same as the one bit scheme except for storing two bits (seems logic

I seem to be missing something when the two bit scheme is introduced it's said that it's the same as the one bit scheme except for storing two bits (seems logical), but then the index in the lookup table seems to involve both the branch index (already the case in the one bit scheme) and the branch history (as far as I can see never introduced).