We are currently hosting a Skip Barber server and want to restrict people to only join using the 'national' version of the car. So we removed all other vehicle classes ('Skip_Barber' and 'Skip_Barber_Regional') in the dedi window when starting the server. The problem is that drivers can still join with the 'regional' version despite using the vehicle classes filter. You might say it's an improvement over getting booted as described here and here and I most certainly agree. But it would be best if the filter actually worked and drivers only had the national version of the cars to pick from when joining the server.
Yeah, we worked around it with a server-message upon join explaining they need to get the correct car. that worked for us.