Maybe A-bodies used a different painting process...or maybe the painter was just cleaning out the gun. My Challenger had very little overspray on the inside. The body dip line was clearly visible. Maybe Dave Walden will see this and post pics of this cars for reference?
Maybe, but I don't think so. This is the floor of my '71 Dart GT (yes, another A body). Although worse for the wear, you can see that it had full coverage on the floor. The shifter bracket is oversprayed, which tells me they intended to paint the floor but didn't change the angle of the paint gun to get the bracket. The Duster was built at the St. Louis plant, the GT was built in Los Angeles. My EL5 GT, built at the Windsor plant, as equally good coverage on the inside. It also has pretty darn good coverage on the bottom too, unless you actually roll underneath you'd think it was painted.
To get away from the A bodies, this is part of the floor on a 1971 Plymouth Satellite Sebring Plus (B body) built at the Los Angeles plant. Although this obviously isn't the entire floor, the coverage of the paint tells me it was intentionally sprayed, and I suspect if I pull up the rest of the carpet I'll find that the entire floor looks about the same. This is also the original paint.
My Challenger does not have that sort of coverage, but its been re-painted. The tunnel on it is primer black, and I assume was part of the respray, so its not any help. I'm sure it varied by plant though, as pretty much everything Mopar did varied more than a little from plant to plant.