I you look at the Dev Diary on diplomacy as an example. We have aimed to do two things HoI3. One to allow the historical result to happen. We know this did happen, so thus it should be able to happen. However we have also tried to have the system work in such a way that ahistorical outcomes are possible. So it is possible for the Soviets to align Yugoslavia with Comintern, especially if no one else does anything to prevent it.