They iterate even more out of the public eye. There are endless reams of concept art that never even made it to scale model clay. All of the major manufacturers

They iterate even more out of the public eye. There are endless reams of concept art that never even made it to scale model clay. All of the major manufacturers have design houses staffed with people who's sole job is to draw neat looking car ideas. Eventually a few float to the top and they make scale models out of clay (or in this day and age on rapid prototype machines). And then those design studies may end up as full sized, half-car (lengthwise) mock-ups made out of clay. If they survive that, they may even get made into a pure, non-functional concept car like we see at trade shows. It the public reception is positive, they turn manufacturing engineers loose on the design and they cut out all the artistic junk that would cause the car to cost 4 times as much to make, and introduce safety devices and such that change the styling.....it might make it to a functional prototype at that point where they show it at next year's auto-show, if reception is still good, it'll probably make it into to production.