On a privately owned or tourist railroad owned piece of equipment, I would agree 100%. On a piece of equipment displayed at a national heritage site that just underwent an extensive restoration with great pains taken to get every detail right to a specific time period, I am not sure it is acceptable to have a glaring error on one aspect of the lettering. (Especially when the error is so noticeable and so easy to fix).
The Cimarron bridge exhibit is probably the best display of a steam locomotive in its natural habitat in the entire US, every other detail is right, why not fix this one?!?
Jason Midyette