It's always difficult to judge condition, originality, etc. from pics vs. in hand.
This is a Model 1917.
Model 1917's were produced with plating. I'm aware of nickel and gold. See Bailey's book if interested.
Bailey also has a factory pistol with a nickel slide and blue frame. So mixes are possible, remote, but,...
Generally after market plating can be detected in barrel stamps and/or other stamped markings. Also rounded/buffed edges vs. crisp edges is a clue that some restoration has occurred.
This pistol is certainly dolled up. Has a mismatched screw as someone pointed out, some kind of tag within the magazine area and looks well used.
A factory letter generally indicates whether or not a piece is/was plated, deluxe, engraved or other.
A pistol (or rifle) may not have a ledger entry at all. Speculation "could be" a special made of a dignitary, salesman, lunch box special or other and not recorded in the normal production system.
Add it all up and unless a compelling reason exists as to why this pistol may indeed be a factory special I would not pursue for the above reasons.
I do possess non-factory pistols that I just liked, so I bought them. A fellow could do the same here.
Buy it, letter it and report back.