The Colt 1909 is a Colt New Service, made for the government as a stop-gap service pistol until the 1911 could be perfected.
It was made for the Army, Navy, and a FEW for the Marines.
These revolvers were numbered on the butt with US serial numbers, and Colt added New Service range numbers on the frame under the barrel, on the crane, and inside the side plate.
"Assuming" Number 42XXX is the FRAME number NOT the GI number on the butt, it was made in 1911.
The numbers that year ran from 29800 to around 54499.
The info comes from the official Colt factory records as published in R.L. Wilson's book, "Colt: An American Legend".
In the back are official Colt serial number records for all Colt firearms up through 1985.
The same numbers are in the web site, but it only goes to 1979.
As above, the 1909 numbers are lumped in with the New Service, as is the Colt Model 1917.