Sorry, I cannot resist another word or two on the topic.
First, a number of the large railroads made steam locomotives to their own design in their own shops. Also, when it came time to rebuild or repair a locomotive many more railroads would made their own modifications to the locomotives they bought from other railroads and from locomotive builders. Since we have our own railroads we too, can make and/or modify the locomotives and rolling stock we own any way we want. We are simply following prototypical practice, just on a smaller scale.
Second point: How realistically functional our productions appear depends on a number of factors. Some of us know a lot about how a steam loco functions and can make rational designs and modifications of our own. Hooray for us.
On the other hand, some of us modelers like to make whimsical designs which would never even stay on the rails if produced in full scale. But so what? This is our hobby and we are making our models for our own enjoyment. Yes, what the whimsical guys make will bother the knowledgeable modelers a bit, but, again, so what? We are making our whimsical thingees for our own amusement and enjoyment, not for anyone else. Its a hobby, remember? So a big Hooray for the Whimsical modelers.
There is another group of modelers who make their own designs and modifications, trying to make a realistic locomotive but get it all wrong because of their lack of knowledge. This type of model can bother knowledgeable guys because we see it is wrong and it is not meant to be whimsical. 'Tis neither fish nor foul, it is just wrong. But once again, So What? The modeler made it and he is happy with it. Personally, I may very gently ask him delicate questions about it, like why does that steam pipe come out of the head light? If done nicely one can encourage the builder to make his model closer to reality. But should we interfere with his fun? Why burst his bubble? That is a question that is hard to answer, kind of like telling a guy his fly is open when he is speaking in front of a group of men and women. I do not know the answer to this one. I saw one model where the guy put floats onto an model airplane that never had floats in reality. The idea was OK but the floats he used were way too small. It was obvious he used whatever floats he could find out of ignorance or sloth. I did not say anything when I saw it but it still bothers me today. Well that is my problem and I have to live with disturbing things like that. But, it is his hobby and all I can say is I would never say anything about it, unless he asked me personally for my opinion. So it is live and let live, I guess.
In effect, all we can say about what a model should be like is how we personally feel our own models should be. In a hobby we really cannot tell anyone about what he should be doing. It is, after all, just a personal hobby.
____________________ "I am not a grouch. It is just that I am right and everybody else is wrong."
J. Pierpont Feathersbottom, Esq.