Let me answer your question: "how would two people who do not know each other, have full access and ownership to the exact same vehicle?"
Well it is not the same vehicle. The imported vehicle is bind to account. That means each character that I have on that account should be assigned with a car like that. Probably you will say, nice you import one and because you have 3 characters then you get 3. Wrong . You can not be logged with more than one character , so at anytime in fact you are using only one imported car.
An account can have multiple characters which don`t share things. So, as long as I buy credits and those are assigned to my account, then everything that I buy with those should be assigned to my account. For ie VIP, the VIP is bind to account, even if you are on a character or another you benefit of the VIP perks.