Note - I'm still running offline server 1.7. There are a few missing cars and I'm wondering if it's just a matter of getting codes, or if entire files are missing. The cars I'm noticed not present are the rental version of the Dodge Charger Elite, which has a bit higher performance and better handling than the standard charger. I don't remember if any other rental only cars had unique setups. The other missing car I noticed is the achievement version of the CCX, which I do have in my profile since the profile was downloaded before shutdown, but the achievement version of the CCX is not in the car dealer. There may be other missing cars.
So it seems these "missing" cars may be there in the program data files, but just not included with the dealer.