I decided I had better do a fact check on the info in the reference book I used; The Standard Catalog of American Cars 1946-1975. So, I asked Google; "When did the 5-mph bumper law go into effect?"
Here what Google AI generated:
The 5-mph federal bumper standard (Federal Motor Vehicle Safety Standard 215) went into effect on September 1, 1972, for the 1973 model year.
Hmmm. Well now I need to double check my memory. So I did a search for pictures of the '73 Camaro. And all I could find were ones that had either the full-width thin bumper, like this;
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Or the thin, split bumpers at the corners, like this;
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I could not find any 1973 versions with the massive bumper that the '74 model had.
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Now, what I'm not sure of is whether or not those '73 bumpers were mounted to those energy absorbing shocks (or whatever they were called). But even if they were, I can't image they'd protect the headlights much.