The 1981 (and maybe the 1980) also have round turn signal indicators instead of triangular. Also, due to the new international symbols, the trim plate for the rear defogger has a small, rectangular hole for the defogger identifier (which lights up).
Back in the day, they did things that don't make any sense today in regards to production. For example: In the 1969 Grand Prix, Pontiac engineered and produced unique seat tracks and frame, seat pads and upholstery; DASH; glove box door, interior and lock; steering column, shifter and shifter linkage just for the few people that wanted a bench seat instead of the standard buckets. (with bucket seats the shifter was in the console and there was no glovebox in the dash.)