The Occupation of Belgium

The German plan of attack in WWI called for a quick war to knock out France while the Russian army mobilized, thereby avoiding a two front war. To do this they created The Schlieffen Plan which called for the German Army to go around the main French defenses on the French-German border by marching through Belgium. When the major opening battles were finished the Germans were left in control of most of Belgium, and they installed the General Governorate of Belgium, a military system to administer the country. That's where this curious book comes in...

click to enlarge

The text on that page roughly translates as:

Law and Official Gazette of the occupied territories of Belgium

contains
the
laws, regulations and notices

from 1 january to march 31 1917

(from nr. including 295 to 327)

Brussel

published by the political department at the Governor General in Belgium. To be obtained in Belgium by the print shop of the Act and Official Gazette, Brussel, lowenerstr. 40 in Germany and in neutral countries by the German post offices

This is a journal of the "laws, regulations and notices" passed by the Germans controlling Belgium. If you look at the photo again you'll notice that there are two stamps in the top left corner by the General Staff Library in the War Office on 30 April and 17 October 1917, which means we know this books was printed and published during the war. This begs the question: How did the British manage to get a copy of this while the war was still being fought? Any ideas?