Playing as the Eastern Entente, I've noticed To End All Wars has fallen in the same trap as many other WW1 wargames in having Finnish divisions and corps in the Russian army OOB.
In real life, there were no such formations. The Finns were not required to serve in the Russian military.
Finland was something of a special case in the Russian empire. In 1809, after having conquered Finland from Sweden, Tsar Alexander I made Finland into an autonomous Grand Duchy in order to prevent any rebellions and to quickly win the hearts and minds of the Finns in a dangerous international situation (the Napoleonic Wars).
Finland had a small military of its own in the 19th century, and some of those units took part in Russian military campaigns, most notably the Russo-Turkish War of 1877-1878.
Everything changed when Nicholas II came into power at the turn of the century. A so-called Russification policy was begun in Finland, the goal of which was to integrate Finland better into the Russian Empire. The Finns responded to this pressure with various means, ranging from peaceful demonstrations to political assassinations. As a result, the Russian authorities began to view the Finns as dangerously disloyal and unreliable subjects of the Tsar. It was seen as unacceptable to allow the Finns to have their own military, and so the last units of the Finnish army, the Guard, were disbanded in 1905.
When WW1 began, the only Finns serving in the Russian army and navy were a few hundred volunteers, many of them in high positions, like General Mannerheim.
The Finns were required to pay war taxes and provide industrial products to support the Russian war effort, but they were never required to send their men to fight in the war.
In order to make EAW more historically accurate, I suggest that you remove the Finnish nationality designations from all the Russian divisions and corps that currently have it in the game.
There must be an erroneous book or some other source somewhere that contains a Russian OOB with these completely fictional Finnish units that simply did not exist in real life.
It's common knowledge in Finland among all the people who know at least a little bit about our history as part of the Russian Empire that Finns weren't required to serve in the Russian army in the Great War, so I don't think there's even any need to provide you with sources. In any case, they would be in Finnish.
All you have to do is to remove the Finnish nationality from the Russian units in the game. Should be a relatively simple change.