J reg's are H plate shells that were sat around for a bit. Mate of mine insists he's seen one on a K plate in Soton, but I never have. Lates are normally good as they have all the toys (late H GL's especially) as they just seemed to have been clearing the shelfs!

There are a few Js about if you look hard enough.

I did once see one on a much later plate....M or N. It must have sat around unregistered for some time. It does happen - a guy I know has an S plate 850.

cheers

James