this would be much easier in a state that was AAA-#### as there'd be a much more even distribution of numbers
California is relatively close with #AAA###, I remember using spotting new first # as an indicator as to how many cars had been bought.
Yep, my parents purchased a car in 1978 that was still on "NNN AAA". Then our next car was a 1986 model, and I believe it was a "1 AAA NNN" series. By 1993, I purchased a car with ridiculous vanity plates, so I immediately pulled them off and registered normally, receiving a "3" series plate.