Four different front bumpers were put on a 1971 Challenger three different back bumpers. Rallye dash Tach after around June 1st is different than ones before. There were a lot of changes leading up to the 1972 Model and Plymouth and Dodge had different times when they changed things. The trunk floor pan change for the rear access shock hole change came first in a Challenger weaks before Barracudas. There are other panels that were changed before the end of the year and during the year that stayed into 1972.