Single "R" prefix
Replacement always used weight/type code in conjunction. Some long-time collectors contend that "R" was used for government plates. If I confirm this, I will move these to the Government section.
U, V, W prefix
One long-time collector says that "U" was used on School Buses exclusively. My research has pointed to V and W were used on Government vehicles; I'm still trying to separate if certain codes were used on certain types of vehicles (government bus, truck, trailer, etc).
strange prefixes that don't conform
1963 - 2-letter prefixes did not begin until 1964. Personalized did not begin until 1972.
1964 - Sample plates were always in format A-00-000; is this a prototype/color test?
1965 - Sample paltes were always in format A-00-000 or SAMPLE; unknown what FB prefix stands for