How important is the data plate on the firewall in the engine bay?

[hawgcaller]

I am looking to buy what is claimed to be a 1946 wagon. This guy says that is the first year that they produced them. He also says that there is no concrete data as to how many were built then. He says the data that is posted on line is incorrect. What do I believe? Please help.
The Data plate in the engine bay is gone.
I see data plates for sale, so how important are they?