Occasionally in the USA you find watches advertised as being in a "Salesman's" or "Display" watch case that has has a transparent back so that you can see the movement working.
I am a little suspicious that these were not actually for salesmen but I should have been more suspicious of the American watch with such a case I bought in UK where these cases are very rare and never seen on English watches - at least I don't recall seeing one - not least because English watch case construction does not generally lend itself to the form.
Here are the front and back of the case in question side by side.
If you look at the enlarged version of the picture, by clicking on the image, you can see more clearly see that the front bezel on the right has a very worn pattern on it whereas the one on the left does not. What has almost certainly happened is that someone had a watch with a damaged screw-on back and they found an almost matching front bezel that fitted the back and we suddenly have a more valuable display case.
The main body of the watch has a different pattern on it so it is even possible that the case was constructed from three different cases!
I must try and study the pictures more carefully but it's difficult when you are looking at several hundred in a sitting.