AHA! So the "C" means the "odometer" has "gone around" already, so I was close!
Useless Unrelated Fact For the Day: the same thing happens with Massachusetts car dealer license plates... once you go from plate EXAMPLE-A through EXAMPLE-Z, you start all over again with EXAMPLE-AA. SO any dealer plate in MA with -BA or even -CA has lost a LOT of plates through the years OR has the same number for each location.