Hi Valentin,
I am replying on behalf of Len Boydell, the Douglas Club machine registrar.
We have checked the numbers of the bike, according to the works records the engine is definitely from 1917.
We are not so certain of the frame numbers around that time but the evidence suggests that your number would have been late 1916 or early 1917 so with the engine being 1917 I think it is safe to say that the bike is 1917.
Much of the confusion of the 2 3/4's of that period is due to the fact that during the first world war many damaged bikes were repaired using any undamaged parts that were available. Some of this work was done back at Bristol by the works, but of course some was undertaken in the field by the military, keeping accurate records of what was done was unlikely to be that important at the time!
How the bike came to rest in Bulgaria is a mystery, but if the bike could only tell us, it would make a very interesting story.
Please continue to bring the old bike back to life it certainly is a survivor.
I have not checked if you or your friend has joined us in The London Douglas Club but we are now the world wide owners club with members in many countries, we would welcome you into our ranks!
Details fo how to join can be found on the Club website
www.douglasmcc.co.ukDave.