Rrrrrrr, need help on this one.

You cannot "believe", "think", "assume", "guess" or...........I've run out of terms

CHECK IT A and B bodies ARE NOT DIFFERENT. The break was 69/ earlier model year vs 70/ later model year.

Calling this whatever 'the middle terminal" is not helpful and not descriptive. You have either 1 field terminal and the other factory grounded, or you have TWO field terminals, both insulated from ground. If you ground 1 terminal, this "converts" it to a 69/ earlier alterlnator.