I think they'll just do whatever serves the current movie plans. If they want certain characters they'll either already be at the school (with no explanation of how they got there) or they will be introduced during the movie. They only have to adhere to the continuity featured briefly at the very end of DOFP - anything else is immaterial.
It may come out that 'something similar' to the events of the other movies happened, but probably not - why complicate things for themselves ?
It may come out that 'something similar' to the events of the other movies happened, but probably not - why complicate things for themselves ?