The position/mounting of the LB and RB buttons on the motherboard piece between the day-one/sans-jack and the newer 3.5mm jack (non-Slim) boards are completely different.

The older revision motherboard has the mountings inverted (pointing downwards to the south end-headset attachment port- of the controller) compared to the newer ones.

The newer ones have the circuit with the bumper buttons mounted pointing to the north end toward the bumpers on the top of the controller.