As I recall, the old JCWhitney catalogs they used to send me had several types of "Built Especially For" dash plates in it. This was back in the earlier 1960s!
In a very few cases I can recall, there WERE some OEM factory plates available on a very few cars, over the years. NOT an option, but part of some promotion or such. Just something different to make the new owner fell a bit more special, if that really mattered. Not unlike the Cadillac grille badges with the number of Cadillacs the owner had owned (which few people knew about OR cared about, much to know what they were looking at on the car).
Seems like that every so often, a vendor would appear at the parts counter wanting us to buy some of those "Made Especially For" plates to give to special customers. Never did buy any of them. FWIW
Just some thoughts,
CBODY67