I'm holding a friend's 9mm Luger from an estate, and I'll post a photo, if necessary to help with value.
In the meantime, I've perused this site some, and can't find a reference to a Luger marked 1913. The production information on this site jumps from 1908 to 1914.
The serial number is 18xx o , it's built with mis-matched parts and has been re-blued. So I'm pretty sure that it's not worth a lot of $, but what about that 1913 production date on the receiver?
Or did I just not read far enough on this site?