I don't know if it's an easy modification, but it would save you a lot of work at EOS if you can move the New Sponsor event so that it occurs/appears only after teams are in their correct divisions for the new season.
If this is already on your "to-do" list, please go ahead and delete this thread!
Yes, it was forgotten. The calender was disabled (to avoid teams subscribing to races already in the wrong division), but sponsor was overlooked. Normally the promotion/relegation is automatically done, but now it is done manually and so things are overlooked.