It's a lovely little engine. I think it was a 500cc from 1911 until the Model H in 1914 which was 550cc & the Triumph that went to war (c.30,000-40,000 to the military, I think 40k closer - 30k to Britian & the rest to CND, ANZAC, etc. )
I know there are #s for every Triumph made, I forget exactly where (likely more than one source) but I doubt you'll have much trouble accessing them. It is a relatively common bike (for a 1912) I may have some production figures, will check.