67-73 Abody frame Rail and Rad Support

I have wondered about the shock type bumpers versus the standard bracket bumpers on 1974 models. I thought it was likely a change that took place partway through the model year. I assumed that the later builds would all have the shock type since all 1975-76 cars had them but I have seen/owned early built cars have the shock and later builds have the traditional design. It has always confused me. I thought that maybe there were different assembly plants working on different mandates ??