I bought aftermarkets. I know they were the same Guide: SHERMAN CCC45050L Quarter Panel FORD MAVERICK (1970 - 1977) MERCURY COMET (1970 - 1977)
The only difference through the years on FORD FACTORY rear quarter panels are holes drilled in the back for either the rear valence (1970-1973) or the plastic side bumper panels (1974-1977). These holes can be welded up or drilled to interchange the quarters through the years.
And keep in mind that the aftermarket quarter panels will work but will need some additional work as they aren't 100% direct replacement like a NOS one would be