Nice one Daren. I think a couple of years post-1913: an obvious pre/post 1914 difference is the rear stand pivot, and in the wartime photo the stand pivot is below the rear axle, suggesting 1915-on. 1914 and before the pivot is actually in the chain-stay tube.
Here in Australia we use Dec 31, 1918 at the veteran cutoff date, so we don't worry so much about the 1914/15 differences. More important in the UK!
Cheers
Leon