As Gerald C said, "Let it go".

If you were THAT concerned about the car, you either should have kept it or sold it yourself, not trade it in.

Chances are good that it wasn't sold to an individual who's now driving it, it was probably wholesaled to a wholesaler who will then re-sell it again to another used car lot.
I too work at a dealer and few used car sales managers want to keep and re-sell older cars these days because there are usually too many problems after the sale thus not very profitable. If not wholesaled and the car was nice, sometimes an employee or friend of a salesperson who's looking for such a car gets it.
Any items left in any traded/sold used car are the property of the person or store who bought it and that's just the way that it is.