Topic: 71 to 73 difference

[1969 Cale II]

My current project is a 73 coupe. Needed metal work in the rear, what is the difference between 71/72 and the 73? Many parts are the same, bumper brackets are the item. Bumper/ taillight panel, inner bracket supports are the same, why not number brackets? Or does NPD have a typo?

[67gta289]

From the MPC world, D1ZZ-17787-A & D1ZZ-17788-A for 1971-72.  D3ZZ-17787-A & D3ZZ-17788-A for 1973.  The illustrations look very similar, but to state the obvious they must have been different and did not interchange.  The 1979 OSI manual does not list either the D1 or D3 variant, which is an indication that the D3 did not supplant the D1.  Both were still available as of the 1979 printing. 

There were of course 5 MPH impact requirements for bumpers, so I expected to see something obvious on the 1973 diagram that would account for this, but I don't.