They were sold at train shows that grew into a mail order business. I have built most service branches and most eras but mainly U.S. Army WWII and Korea.
Modern military is very limited.
The difference is in the details and finish. These cars are debarking from the factory to the military base or war zone. These cars are debarking the training camps, field testing facilities or battle zones to other zones of operation. They have seen action in the field. They have encountered heavy action and damage, if not totally destroyed.