It is actually safe to say, that ANY type of prototype which was built in the past, is still in existence today.
That is to say that, if a 1936 "farm tractor", for example, was once built in that era, and was used then in it's "heyday", then yet they still exist in the front of farmer's homes and in museums and displays. I see it all the time.
Therefore I do not see how dating a model would be detrimental to the consumer, or adverse to their wanting to purchase it. I actually think it would enhance purchasing.
All "dating" would do is define for everyone the date of it's origin and supply "period modellers" with that basic info, and refer "others" to the concept of that, "Yeah! My 'Grandad' used to have a tractor like that! I want to put one in my 1950, or even 1999, railroad scene."
What would "label printing costs" be?; an extra 1/1000 cents/per?
Paul Hillman