As a point of clarification for the YOM program in California, one needs to understand that here in the Golden State the last time all vehicles received a new set of plates at the time of registration renewal was in 1963. Thus original 6 character 1963 series plates (the Black and Yellow ones) are still considered valid and current on any car that has had them since 1969 or earlier when DMV ran out of the black and yellow plates. The blue and yellow 6 and 7 character plates that started being issued in late 1969 are also still considered valid even though DMV stopped issuing them near the end of 1986. Consider that DMV has been issuing the 7 character white and blue plates for more than 30 years. The key point being is that no standard plate issued since 1963 has been superseded by the next configuration.
This is contrasted to many other states were new plates are issued more frequently, superseding the prior series of plates. Lastly, with few exceptions (like personalized plates) plates are issued to the car and not the person so they follow the car for as long as they exist and the car remains registered. Thus the requirement of being "clear" in the system requires that a particular plate is not still shown as being assigned to a particular car currently.
The YOM program here was intended to allow hobbyists willing to jump through hoops and pay additional fees to do an end run around the standard plate assignment process and enjoy the appearance, if not the illusion, of California provenance implied by having an "original" plate on their vintage car.
I have seen a few of the new black plates and they have all been on non-vintage cars, the first one being a brand new black VW Jetta.
*Principal wrench on this 69 Mach I*