Here is a 1951 CA motorcycle plate, no year tag added. This plate can be retro-fitted to any motorcycle titled as a 1951, as long as this particular number sequence is not already in use. Each time CA switched to a new base plate, everyone had to get new plates, and the number sequence started over. So base plates from different eras could have the same number sequence.
Here is a 1951 motorcycle base plate with a 1954 year tag
Here is a 1963 passenger car base plate, with a 1965 year sticker.
1963 was the last time CA made everyone with currently registered vehicles hand in their old plates and attach new plates to their vehicles, with a new number/letter sequence assigned. From then on, each yearly renewal meant attaching a new sticker. When the AAA 000 sequence for cars reached ZZZ 999, CA switched the sequence to be 000 AAA, and also changed to a blue background. This occurred around 1970. When that sequence ran out at 999 ZZZ, CA switched to a 7 character sequence, 1 AAA 000. When that reached 1 ZZZ 999, it rolls over to 2 AAA 000, and so on. We are currently at 8 Txx nnn. There is much speculation about what will happen when 9 ZZZ 999 is reached.
Many years after 1963, people advertising vehicles for sale would specify "CA black plates" in the ad. This used to be very prestigious. This meant that the vehicle was still registered with the 1963 base plate. For cars built and sold prior to 1963, or that were built up until the blue plates started in 1970, if you were selling a car in the 1980s or later, still having the CA black plate from the 1960s was an indication that the vehicle was relatively rust free, as the assumption was, the car was stored or used in CA during all those subsequent years. THIS IS NO LONGER TRUE, since 1960s plates can now be retrofitted to any vehicle titled as a 1963-1969/70 vehicle now owned by someone in CA, whether or not that car was originally sold in CA.
Here is a 1970s era blue plate, from a passenger car, with a 1980 renewal sticker, spotted at the VOC Annual Rally in 2012. The owner told me the plate was found in the UK at a breakers/salvage yard. That type of plate, if you have or buy a matching pair (since CA requires plates on the front and back of cars), with a matching renewal sticker from the 1970s, can now be retrofitted to vehicles titled as as a year from the 1970s.