Generally speaking 1916 & 1917 lugers are the only ones dated.
We need more information to determine what variation you have and to help you date it. A picture is worth a thousand words!
If you can not get a picture, FGS has a few Navy's for you to compare variations and also prices.
PLEASE, PLEASE be careful on your first Navy purchase!!!!!
Fakes are everywhere--everywhere! Let us help you!
Vern
http://fgsfirearms.com/