Pictured in my 1971 Parts Illustrations Manual are the PN 9774609 "Pontiac Motor Division" caps for all 14" wheels from 1964 to 1969. Then for 70-71, it says 9774609 except Firebird, and PN 5738083 for Firebird. Can't answer later than 1971, and there is no different photo of the other part number cap.
Personally, I never noticed the difference before.
Glenn Uettwiller
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A friend is someone who knows the song in your heart and sings it back to you when you have forgotten how it goes. --- unknown