The game did not go historically. Historically Poland was overrun in a month. It was all done and dusted by mid-October. In the game, Daniel held his ground admirably, retreated incrementally with great timing, skill and coordination, ahistorically received direct aid from the Allies, and held off the end of Poland until January 1940. That alone took events out of the "historical scenario," which meant the USSR in turn was in it's rights to respond ahistorically and not get involved.
The "historical scenario" may have pre-requisite rails - but they are not unjumpable.The Ai still apparently adapts to the in-game events. The more the player does to change the historical timeline, surely the more likely it becomes that countries affected by those changes will themselves go ahistorical.