As far as I know, the people who can enforce it are the copyright holders, if they have evidence that BMW isn't complying with the license. It's irrelevant whether they personally own or have used a BMW car.
If BMW (or anyone) has distributed the code in violation of its license then the copyright holders can sue. But there would have to be someone who's received a BMW car (i.e. distribution) for there to have been distribution in violation of the license.
Sure. So the question then becomes did they a) fail to include the required written offer with one of those cars or b) not honour that offer for any third party? And the answer to both of those is no.