Mike
This is the second 1915 DWM with Erfurt style test proof on its right receiver that I have become aware of in the last few days. See links below;
http://www.gunbroker.com/Auction/Vie...Item=104501382
http://luger.gunboards.com/showthread.php?t=15262
It is unusual but sometimes happens. For more information see page 37 and 55 Central Powers Pistols.
Jan