Mark, you bring up a very valid point, the show cars NASCAR teams use for promotions at your local car dealer or supermarket are just like you said, an older car "modeled" after the current car. I've had the honor to speak with some of the show car drivers of a few NASCAR teams, and have asked about the cars, and that is always the answer. They take a older chassis that is either outdated or not raceworthy, take an older engine and really "make a model" of the new car.
Holy slippery slope, Batman. When they do F1 PR shots, or the "presentation" press releases, the line between "model" and "real" is blurry. Often the cars are a spare of last year's "real" race car dummied up to look like the new one, or a prototype/test car that isn't in driveable condition anymore. But only a handful of people know for sure, since sometimes the cars shown are real-deal racers.
The slippery slope in this case, most of these "model" showcars might be "reissues" of older cars for new versions, but most all of them I've seen, the driver of the show car hauler is usually on his own, and drives the car into the trailer! They may be models made from older cars to represent newer cars, but when that "old" engine fires up, there's a REAL shake in the ground!!!!