Re: 1917 German Luger
Lugers are one of my passions... oh, and my wife is a passion too... just in case she reads this.
1917 was near the end of WW1 and many Lugers were parted out. Some were junked (shame) and some were rebuilt using the parts and were re-stamped 1920 under the 1917 which was left intact. Most of these do not have matching numbers. When you find a double date Luger with matching numbers it is likely someone has gone through a bunch of parts and come up with the correctly numbered parts or has restamped some parts so they match. Either way is silly as the double date Lugers are collectable as is.
With most Lugers the three main considerations for value are condition, condition, condition... with rarity coming in an important fourth... with carbines at the top of the heap and artillery models next.
WW2 came along and Lugers were date stamped with codes for the year as were Mauser rifles and other Nazi guns... I guess they thought this would help win the war... or confuse us, or something.
A really good pic would be required to put a value to your Luger.