As long as the spec hasn't changed why does it matter? All that counts come resale time is the date it was registered.
You've also got some extra cash off. result!
If they've only registered it in the last week or so, then that would be very silly, as you could have hung on a couple of weeks and had it reg'd on an 11 'plate. Loads more cash come trade in time.
Whatever, Its still a "new" car. I wouldn't lose any sleep over it.
I think you'd be very surprised at the amount of "new" cars that are months and months (and some even years) old before being registered!
Thirty four long weeks down...Now it's here !