Well, your dissertation on the word "proper" is all well and good.
But I never used the word "proper" nor did anyone else in this discussion to date. But I do get your point.
I already knew the Master Car Builders preferred running board(s). Maybe somebody else has an authoritative reference for roof walk. (Athearn doesn't count.)
Sill step vs. stirrup I wasn't so certain about and you appear to have a strong reference source.