What a good find!
I can not specifically answer your question, but can throw out a few observations based on handbooks for other years. I have originals, reprints, and/or photocopies for 1909, 1911, 1912, and 1913 Working Instruction/catalog/spare booklets for the early 2-3/4hp. For 1914-17 all I could locate at the time were photocopies of leaflets, brochures, and magazine extracts of the various models; this when I was gathering information to update the Douglas Timeline and Model Identification charts on this Forum. (I need to do another update, so if anyone can fill in the gaps please get in touch.) The photocopies came from the VMCC archives in the UK, and the reprints from John Withers in Perth. (The later I see has a full 1916 handbook reprint available that I did not notice before, I'll have to get one.)
The full handbooks from 1911-13 are about seven inches high and five inches wide (they vary a little), and run 80, 112, and 126 pages respectively. 1913 is the first year to have the fold out diagram. The 1911 and 1912 are cardstock green-gray covers, and the 1913 is more gray-green. So your 1914 does not continue the trend at 47 pages and with a black cover unless they decided to slim down the publication. Since I do not have a 1915 handbook to bracket it with, it is hard to say for sure.