You might find this useful, or at least interesting. I still thought '74s had fat bumperettes. But it does suggest inconsistencies between even having bumperettes on the front and/or rear.
The part #s are a bit confusing, but the catalog listings show a change date of 11-14-73 for the fronts. So that would be a few months into the 74 model year. I believe the rears changed earlier in 73 or maybe with the model year.
