For the 1971 Barracuda, I have always known of the BH23 and BH27 body style designations in the VIN, but I just noticed in an old 1987 Standard Catalog of American Cars 2nd edition lists a BH21 2-dr coupe in addition to the BH23 2-dr hardtop. Was there a BH21? How is it different than the BH23??