Correct; emissions requirements did become more 'strict' in '72, but they did not 'start' in '72 as you originally intimated. The separate evaporative emissions tank in your left rear fender well was a piece new for '71.
(Ask any of us that were there when the '71's were new; the emissions equipment issue was already a reality...)
Need more examples? Take a look at the complex smog pump set-up on late sixties Camaros and Mustangs.
Exactly. Emissions controls where already coming in during the late '60s, and they just gained emphasis as the 70s wore on. This idea that the muscle car era "died" in '72 in silly. It's an arbitrary "line in the sand" that's been invented by the so-called experts and magazine editors. After all, the term "performance car" is relative. I don't recall anyone being that hung-on on dates back in the day. All anyone cared about was how your car performed on the street or strip.
