[gassit]

I believe this is not quite correct, there is an additional step. Once you enter the VIN BMW ConnectedDrive will send a message to the car which you have to retrieve through the iDrive interface before it will 'pair' with online services or the app. You need to have physical access to the car.

And if you sell the car and it is added to another ConnectedDrive account (or BMW mark it as sold) it disappears from your dashboard and you need physical access again to add it.