Obvious when you think about it but this is just current plates available for order, and lots of states (all?) let you keep old plates around as long as you want and they don't fall apart or something. Virginia used to have a few different "400th anniversary" plates in the mid 00s (Jamestown was founded in 1607), which I still see around regularly. I used to still see the even older standard 6 character plates around too -- those are mostly gone by now but every once in awhile one goes by.