Pre-date short-term identifiers

Hello together, short question: This Saturday I can pick up my A5 Sportback, for the transfer I need the short-term license plate. The thing is that the office this week only has longer open on Thursday (that is morning) so I could come by. If I do this tomorrow, the license plate is only valid until Monday. I would have to allow it to be right on Monday. But I am on the road on business! And otherwise I don’t know any person who can do this. On the sales contract it says: Delivery 13.02.16 (i.e. Saturday). Can the office not predate this on the basis of this fact?! That the license plate is valid from Saturday onwards. Online it says that this is not possible. Are there no exceptions? Just don’t understand this, have a perfect proof. Thanks and LG