Here's a comparison between the original 1972 polyethylene valance:
And the 1972 steel replacement warranty valance:
Notice the unfinished look of the mounting area under the beak and the large gap between the top of the steel valance and the bottom of the bumper, this was because the steel valance did not mount to the bottom of the bumper like the poly valance did. (The steel 1972 replacement valance was actually the same valance as used on the 1970 and 1971 Firebirds. The 1972 and 1973 cars came with the poly valance originally).