There is nothing to stop anyone buying or keeping on retention a registration from earlier than the date that the car is actually registered. Unwise of the dealer, but he may have had a batch of 2006 registrations allocated to him and used one of them when he came to register this car for the first time in February 2007. Of course, a February 2007 would be a 2007/56 anyway. It could not be an 07 reg unless registered between March and August 2007.