Hi! There should be 25 different interiors for each vehicle type, but it sounds like you ended up with two vehicles pointing at the same interior, which shouldn't happen.

If the server admin sits in a vehicle and brings up the right-click context menu, there should be an "RV Interior" debug menu with an option to show the assigned interior number for the vehicle they're in. You could use that to confirm that the two vehicles show the same number. There's also an admin option to reset a vehicle, which should force it to allocate a new interior number the next time someone enters the interior of that vehicle, so you can do that to one of them to stop the two vehicles sharing the same interior.

Unfortunately, there's no current easy way for the admin to point a vehicle back to a specific existing interior map. A server admin can use no-clip to pass through the interior's walls to get at all the instances - they're arranged in a 5 x 5 grid with ~60 tiles between them.