You can always go to a VW dealership and say that you disconnected the battery and that later the radio asked for a code. So you just need them to tell you which is it.
With the numbers I told you before they can search the database where the codes are stored. If the numbers aren't right, i.e., if your car isn't the car from which the radio came from factory, they won't find the code. If it works, it's a proof that the radio belongs to that car.