I think you have it covered Steve, at least from my experience. That's how I have them inventoried also, with the exception of your type I. By 'plain' do you mean no herald or lettering at all? Did they come from the factory like that?
I always thought it was funny they didn't make it in green, an otherwise popular bridge color.
How many heralds are there? I know of 6, am I missing any?
Great Northern
Rock Island
Illinois Central
New York Central
Pennsylvania
Wabash
And then the question is, did all the heralds come in all the colors? I've never seen a blue Wabash.