> California switched from the Black w/ yellow symbols license plate to the Blue w/ Yellow plate in 1971.

To clarify, while California stopped issuing the yellow characters on a black background plates, it didn't require replacing those already issued as it did many years earlier when switching from black characters on yellow. Today, Calif has quite a variety of license plates: yellow characters on black, yellow characters on blue, and blue characters on white (reflectorized), all with varying combinations of letters-numbers and numbers-letters. Rather recently it has begun re-issuing yellow characters on black (vanity plates only). I picked this up from the internet recently: there are more registered motor vehicles in Calif than there are in all of Australia.