Difference between 70-71-72 dusters...

ok, lets start from the beginning:

front bumper: some have jack slots and some do not (not sure which ones do)
Grille: 70 used a medallion which was not on the other years. somewhere mid 71 they changed the grille to the 72 type which looks visibly the same but lacks two removable trim pieces. the sharktooth grille was a 71 and 72 option only.
Front fenders: 70 and 71 have the same fenders because the markers are the same. Emblems differed, 70 used a reflective "Duster" decal and some of the very early ones were printed in black and white only. 70 Only also used a "valiant" emblem on the fenders.

In 1970 only: Rally wheels were standard on 340 cars ....71 and up they became an extra cost option.

Body side stripes differed every year.

Dash: 70 and 71 rally dash are different because the radios are different 70 had a thumbwheel and 71 had the knob type
Standard dashes had a different cluster bezel in each year. Some early build 70 had square gauges that resembled a 69 valiant instead of the more familiar round gauges which would become a familiar sight through the 70s

Each year had different seat patterns.
Bucket seats were different each year and 70 only had a unique seat track setup. They resembled the 69 and back type but had all four bolts from the bottom as would become common through the 70s
Bench seats were the same in 70 and 71 with only the patterns different but the frame and track were the same in 70 and 1 .....72 had a completely different bench seat and it would fold flat to make for easier back seat loading. The tracks were unique to the 72 style seat.

seat belts were different for each year.

headliners: headliners in 70 and 1 had the bow type, 72 had a one piece cardboard which would become common through the 70s

71 only had a vapor separator in the trunk. when you open the trunk its on the left hand side in all 71 cars.

Deck lid: 70 and 71 had the same deck lid which had provisions for a Go wing. 72, the deck lid changed because there was now a body line that went down the middle of the lid. The body line added strength and made less susceptible to getting dented in the middle by someone slamming the lid too hard.

tail lights: same between 70 and 71..72 had a one year only tail light.

rear bumper (see front bumper)

There is a LOT more to cover but this is a general overview from what I know of ....I am sure there is still a lot more that I don't know