The war did not officially end until the peace treaties were signed in 1919... 
If you want to get silly about it, a treaty does not come into force until it has been ratified by all the signatories, which means WWI technically ended when the Versailles Treaty was ratified by America in, I think, 1925.
Not so. Treaties usually provide for coming into force for such signatory states as have ratified when a minimum number of ratifications have been reached, and coming into force immediately for subsequently ratifying states. I am not sure what the Versailles Treaty, signed on 28 June 1919, provided, but there is no doubt that one major provision came into force on 20 January 1920, viz, the Covenant of the League of Nations, which the USA, notoriously, refused to ratify, to the eternal chagrin of Woodrow Wilson.
So far as Britain was concerned, as I have mentioned in two recent threads on 1918 electoral registers, it was provided by domestic statute that the Great War was not legally concluded until 31 August 1921. (Anyone who thinks that that was rather late in the day should ponder how long it took for the Second World War to be legally concluded - but that is whole other story stretching to relatively recent times.)
Apropos the 1914-1919 configuration itself (which was, indeed, derived from the Versailles Treaty rather then the Armistice of 11.00 a.m. on 11.11.18), it is not infrequently found in publications relating to WW1, including a number of war memorials.
