Luger Artillery Erfurt Double Date 1917-1920

[2amendment]

I just got a Luger Artillery Erfurt Double Date 1917-1920 chambered in 9mm.
With a serial number 3895 with no letter, only 4 digits. on the frame, the barrel and the receiver.
It is in very good shape with original bluing, and all the parts numbered 95 but the toggle train numbers are 35 not 95 like the rest, the mag has a wooden bottom with the number 661.
I Need some information about it, A gunsmith told me that the miss-mach between the toggle train and the rest is ok because in 1920 the barrel was change from the original 30 cal to 9mm and the toggle is different specifications. Is that the truth?
What is the value of this pistol if I wanted to sell it?
is this a rare item? is double date erfurt a very scarce pistol?
Thanks in advance for the informative answers.