The issue with the blue book is that it goes off of what they have been told. A 1914 is the rarest artillery, if a DWM, and not either an Erfurt or a 1914 model or style (some folks call the artillery a 1914 model) and then say, its a 1914 model with a year of 1918.
So, the 200% would be actually low for a 1914 DWM artillery.
Ed
PS welcome to the forum and I moved this to the artillery section