Hi, BluesBear,
The Model 1903 military (so marked) was a .41 caliber version of the Model 1902. It was strictly experimental, though at least one was submitted to the Army, and they asked for the different marking. AFAIK, it was never given any serious tests, but at least five were made. A picture is in Goddard, Page 82. (I included it simply because it was marked and just to see if anyone would pick up on it. I was a bit astonished to find that someone did!
)
True, Colt at times used those model dates, but not consistently and not, as you say, in their catalogs. They were basically unknown until rediscovered, or invented, by modern collectors. Even factory terms like "Model M" were not commonly known or used until the mid-1900s.
Jim