Yeah, they are updated after every race you participate in. Or every Special Event, or Licence Test, and even Practice mode. If you are bored, and looking for a car, just go practice, drive for 5 seconds, and quit the practice session. When you get back to the menu, you'll have new used cars in the list. Hopefully not a assload of GTOs and FTOs like me

But still no '97 MR2 GT-S for me...