Sorry, Kaylan1, I have never seen WW I establishments, but I suppose they surely will have followed some kind of system.
There is a series of Great War era WE refs in the National Archives Discovery search. They seem to run from WO24/900 to WO24/928 inclusive for 1914 to 1918/19. From the few I've seen online they appear to be very slight documents, a Canadian example is shown here; Researching Canadian Soldiers of the First World War The Nafziger collection lists quite a few, but doesn't shed light on any numbering system. I'll apologise if I'm going over something already explained, but re the WW2 era WEs as far as I know there isn't a single index which lists all WE tables issued, and tells you which WO24 piece they are found in. Each piece has an index that lists its own contents. It depends on whether you're looking for specific tables, trying to build particular formations (my own poison) as to how many pieces you'll need to plough through. Gary
It's a very narrow view but War Establishments: Part I: Expeditionary Force: 1914 does not show any codes for unit WEs. Organization of the Infantry Battalion OB/1919 does not indicate a reference for the Inf Bn WE it shows. However, Provisional War Establishments: Part XXIIIA (Small War) for the Units of a Division: 1923 has unit WEs referenced from XXIII A/1 to A/17. Other formations mentioned in it are: Part XXIV A - Units of a Cavalry Division Part XXV A - Non-Divisional Units Part XXVI A - Line of Communication Units The 'A' referring to 'Small War' WE. WEs for 'Great War' dropped the 'A'.