Libin,
It helps if we get a bit more information. [img]wink.gif[/img]
But I can surmise or guess several things:
1. If it has Interarms stamped, then it is an imported Luger.
2. If it is dated 1918 and DWM, that is what it is, unless there are mismatched parts.
Additional infromation from Technical Information section would help very much on any proofs etc. You can find the tech info part of the forum if you come to
www.lugerforum.com and it is one of the links on the left.