There may be other references that I am not aware of. But many people refer to original california cars as "black plate" cars if they have the original license plates. They were black with yellow letters. I am not sure of the year California stopped making black plate license plates. Probably in the 70s.
In the 1970 model year, California went from 999ZZZ to AAA001. When they did, the plate colors chaged from Yellow letters on a Black background to Yellow letters on a Blue background. Most people, when buying a used car back then, had the option of updating the plates to the current normal plate. (In california today, this is a blue letters on white background with "California" in red.) There are over 20 current plate styles in California. Anyway, when a car is rescued from "salvage," i.e. junkyard, it automatically gets new plates. The indication that it is a "black plate car" usually says that it was first registered in California, and was not brought there from another state unless it was less than 3 years old (in the case of a 1967 'Bird), and was not rescued from a junkyard.
I'm a So Cal native. From cars that either I, my friends or my family have owned, the following first letters on a CA Black Plate related approximately to the following years:
U, V - 1967 W, X - 1968 Y, Z - 1969
What this really means is that the car has been registered in CA all of it's life and therefore the owner can make the claim of "rust free"
FYI Quenton - Black/Yellow plates were Letters then Numbers, Blue plates were Numbers/letters
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI