It has nothing to do with props -- it's the Transportation Coordinator ("Transpo"). Some are meticulous, some figure if it's got the right number and tires and the right color paint, it's good enough.
Some Transpos have an extensive stable of vehicles and accessories, while others use whatever is available from the studio shop when the call sheet arrives, which is mounted or dismounted as needed. The bar used when shooting on Monday (by the second unit) may be somewhere else on Thursday when they first unit shows the stars leaping out of the car. Or it might even be two different cars.
A production with a big budget, or who has a producer or Transpo with a lot of pull, will have equipment dedicated to that production company. Others use whatever they can rent.
The bottom line is that "It's Only A Movie!" Don't trust them to be accurate with ANYTHING, unless you know that they're spending the money to do so.