I think the main emissions reason for the reduced compression in '72 was the requirement to be able to run unleaded gas - which in those days, was only widely availible in regular-grade. I recall back then, and for a long time after, Amoco was the only retailer selling unleaded high-test.
During the '80s, I owned a couple early '70s Audis. The first was a '72, with a low-compression 1.8L four. Replaced with a nearly identical '71 high-compression version. In addition to the extra power, the '71 managed about 4-5 mpg better than the '72 - though I did need to run premium gas!

FWIW, I was in the Virginia Beach Pick-N-Pull this afternoon, and they had a 1978 grey-market/Euro 450SE. Small bumpers & cloth interior. Wonder about the power rating on that one. (All my MB info is back in Alexandria)

Happy Motoring, Mark

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DrDKW