I agree with Bob G. I think your seats were switched, or at least the frames. The frames are identical, both bottoms and backs except for the holes/slots for the tilt rods attached to the knobs in back frames and the sliding track attachment holes for bolts along the seat bottoms.
Robert Hyatt
Williamsburg, VA.
1970 280SL, Red on Silver,4-speed, Euro spec; 1999 C230 Kompresser Sport, Black on Black; 1990 Miata, Black on Red, 5 Speed