thank you Driftwood, nice pics, nice gun.
Not a commercial gun. SO, no "govt model" marking would be on it.
According to what I have been able to find, the "Govt Model" marking began about ser# C3000, on the frame, and was moved to the slide about #C5000.
This puts the beginning of "Govt Model" markings on guns intended for the civilian market at 1912-13.
I also note the British spelling of the word "caliber". There were guns made for Britain in .45ACP. Apparently not all were shipped, and yours likely was taken into US service instead. Alternately, quite possible a slide marked for a "British" gun wound up being assembled into a USGI pistol.
One thing I have learned about firearms, markings, dates made, etc, is never say never.
As noted, the 1912 catalogue does not mention the term "Govt Model", but the 1940 one (the next one I could find) absolutely does, naming the pistol the Govt Model.
So, I stand by my GENERAL statement that the 1911s and 1911A1s made by Colt, intended for the civilian market were (generally) marked "Government Model" But, I also recognize that any, and every variation is possible.