I didn't think there was a difference either until I sat them side by side last night. The one that came out of my car has oval cutouts near the rear bolt mounts and a couple of thin linear, concave ribs on the top surface. The ones I have from a donor car have square holes and a large square indention in the center of the top surface. I assume the large square recess was for the upcoming power seats, seat buzzers and such. I can use the ones I have as far as fit is concerned, but I want to keep all the welded parts as correct as possible.