You're welcome Patric, in fact I think Columbia chain rings presents the same pattern. Check out the "flat" chain ring on your 1918 Columbia Military vs the 1920's Columbia chain ring at the bottom. The ring is clearly visible on the second picture.
Patric if you have any other info on the Columbia chain rings I'll appreciate you share it so we can use it as reference to try to pin-point the year on
@ohdeebee s Indian.
Since Westfield manufactured both bicycles, chances are that the same changes apply to both models, but this is just a conjecture.
Nc