Differences between 70/71 and 72 Darts
Doors are interchangeable, body style by body style, for all '67-'76 A-bodies. '73 and later doors have side impact guard beams, and '73-up 2-door hardtop (Swinger/Scamp) doors have no vent wing windows. Sidemarkers rear and front are different for '72-up vs. '70-'71. Fender extensions are the same. Fenders interchange despite the sidemarker differences. Any '67-'72 Dart, Demon, Duster or Valiant front end assembly will bolt on, and a '73-'76 Dart, Duster, or Valiant front end assembly will also bolt on with some extra work to adapt the bumpers.
If we want to get super picky into the details, the '71 taillight lenses (w/chromed metal inner trim rings) are not the same as the '72-'73 lenses (w/silver painted bare plastic instead of the chromed metal) though the '71-'73 lenses are all interchangeable.