I haven't seen it written anywhere in GMH literature yet, but I think the ones with the plate at the front are for floor shift 4spd with bench seat, whereas the ones without the plate are for console shift (auto or manual) or floor shift 4spd with buckets. The extra notch is to clear the hockey stick shifter that goes with the bench seat.

As a check can you send me the details of all 3 x cars and i'll see whether this rings true for them?