The only visible difference should be the 73 bumpers and any dealer installed antennas. The 72/73 coupes all got the same driver side mirror and polished kidney grille.
There are two different heater controls, 2 have one style, 2 have the other.
The one on the left has a '72 VIN and '73 bumpers.
The '72 and one of the '73s has license plate lights in the bumper. One of the '73s has plate lights on the body. One of the '73s has plate lights on the body and in the bumper, but the ones in the bumper are not wired.
Two of the '73s have one style of headrest, the 72 and one of the '73s have a different style of headrest.
The location and type of the stickers near the engine are different.
I am sure that I could find other differences.