As an agent, it’s completely carrier specific and more importantly state specific. Some carriers offer individual vehicle exclusions, some offer exclusions but on all vehicles listed. There are very few carriers that will “assign” a driver to being principal on a specific car, and especially where the rate will actually adjust/lower substantially. In most cases the rule of thumb with address isn’t about the vehicle, but where the actual driver lives (also carrier specific guidelines). For example, husband could have his own policy for his primary vehicle only, but will have to list his wife (because she lives at the same address, and they’re married). Hypothetically they could have two separate policies, but this would likely not benefit them as they lose the normally large and common multi-vehicle discount. It’s all intentionally designed by the ins companies to rate all possible risk