I see Bill Hirsch lists a 1973-1983 Chrysler Blue engine paint. No 1972. I always thought 1972 was the same as the '73 and up. Am I wrong?

As far as I know, it's the same blue, but I haven't investigated it.
I think the blue started on the "normal-performance" '70 models, no ?

correct! turquoise's last year was the 1969 model year, Chrysler blue was new to the scene for the 1970 model year

A long time ago I bought a '72 Polara with 75000 miles, the original 400 2bbl was painted "smog blue" the same as '73 and later.

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It's officially known as Corporate Blue.