Would you want the region ID attached to the event to override any region ID of the tile? In other words, if the event's region ID is 10 and the tile on which the event is located has a region ID of 11, should the region ID be 10 or 11 for that square?
Similarly, if more than one event is on the same tile and the events have different region IDs, which should have priority? In other words, if one event has region ID 10, another event has region ID 12, and both are on the same tile, how should the game interpret the region ID of that tile?