There is indeed such a law. There’s also a law saying that the state must provide me with a passport after I apply for one, but if their distribution system breaks down for whatever reason I cannot just show up at the passport making factory and demand my passport.

I think it’s obvious that Tesla will be allowed to get their plates sooner or later, and Transportstyrelsen does not seem to be of the view that they shouldn’t be. They are more concerned about the practicality and legality of letting them pick up the plates from the factory.