As much as I'd like you to be correct, you aren't.
Your reasoning is contradicted on one of those pictures were you see the cursor sitting on top of a manufacturer logo and it states "Cars of This Make Available for Purchase at Current Level: 0". On a previous pick, while having the cursor on top of the Mercedes-Benz logo, you can see that the "Cars of This Make Available for Purchase at Current Level: 2". So, obviously, all Premium dealerships are shown there on those pics.
Also, I believe that there are any more premium cars left to reveal besides thoses included on these dealerships. Do the math: The screenshots shows us 51 premium dealerships. Supposing that we would have roughly 230 premium cars (it's a figure based on the generic 200+ number revealed) that's an average of 4,5 cars per brand.
If this reasoning is correct (I believe it is), this means there are no premium cars from Opel/Vauxhall, Bugatti, RUF, etc.
As for the Ferrari cars, (and other brands for that matter) it seems also that the criteria used for making a premium car or not is, somewhat debateable. I fine in having cars such as Fiat 500, or the old VW's premium, but it is hard to believe that such relevant (historically) cars like the Ferrari 250TR, 250GTO, or the 208GTO aren't included (either as standard so it seems).