I believe that the number plate system in Germany is that a number plate is issued to a person, not a car / motor bike etc..Thus, when said person sells said car / motor bike, the number plate stays with the person, not the vehicle.
Seems eminently sensible.
@Andy in Germany would know but I think it's to do with the owner, not the driver. So when you sell your car you take the plates off and if you register a new car put them on that. Or something like that
As
@Dogtrousers says, the system is based on ownership of the vehicle; also, if you move to a different county then you have to re-register the car and you get new plates; counties are fairly small here, so you wouldn't have to move far to need to change plate.
The system for small scooters is completely seperate though, and the plates are different, with a new colour for each year.
Would that mean (say) a couple sharing a car would need to switch number plates each time they switch drivers?
How would it deal with "pool" cars, or hire cars, would number plates have to be continually changed?.
German insurance is for the vehicle, not the driver, so in the case of the van we use for work, I'm automatically insured. A certificate has to be carried in the car and produced if the police ask for it. Of course, if you can't produce a licence, the insurance is automatically invalid.
I'm not sure how this relates to motor scooters.