The Model 1917 Colt New Service differed in several ways from previous made versions, both military and commercial. What I need from you is the actual Colt serial number inside the crane and on the frame, NOT the Army serial number you see on the butt of the pistol.
The standard New Service frame of the period was used with minor changes. The initial "G" was stamped on the grip frame under the left grip, indicating the government contract. There was no Colt proof mark (looks like a small triangle) on the frame. 1917 Colts bearing this proof mark have been reworked and proof fired at the factory. Instead of the proof mark, Army Ordnance inspectors stamped various monograms and marks onto the frame to show acceptance. The "GHS" monogram (Gilbert H. Stewart) appears on pistols up to about serial number 170,000. Then "JMG (J.M. Gilbert) appears on pistols numbered 184,000 to about 220,000. After that, the Ordnance inspector’s marks consisted of the eagle head over a number, usually S15, S18, S19, S20 and "7". This may have been in reference to individual inspectors.
One variation, which I will show you photos of, appears on the barrels of the pistol from serial number 209,000 to about 233,000. It is the addition of the patent date of April 09, 1901. This was a patent date on the adjustable target sights or could have been for some other patent. It was only on these referenced pistols for 3-4 months and was probably due to a mistake made by a foreman in the barrel shop.
Here are the pics, take note of the barrel markings that I was referencing;
http://smg.photobucket.com/albums/0603/Ltcboy/Colt 1917s/?albumview=slideshow
As far as your finish, all 1917's had the wartime finish which was not polished before bluing. The final tool marks were left on the pistol and this resulted on what you see as the "brushstroke" finish. If the pistol has a green or gray Parkerized finish this was done later on, probably during WWII. A few frames have been noted without butt numbers, or with "X" on the butts. These may have been pistols built or rebuilt with a replacement frame. The sounds really dumb, but if the frame was ruined or damaged during service, all parts that were still serviceable were stripped off and used for spare parts. Those parts might have been used to rebuild a pistol on a replacement frame.
Your pistol might have an Ordnance inspector’s mark that was lightly struck or has worn off over the years. Could it be a replacement frame, who knows? Once again, I would need to see Colt's factory serial number on the inside of the crane and the frame.
Hope this helps.
Mike