It already happened for those reference frames, they just haven't been able to observe it yet. For any such beings living there, they don't know about the event

It already happened for those reference frames, they just haven't been able to observe it yet. For any such beings living there, they don't know about the event yet. But when they witness it, they will measure and calculate that the event did occur before today. The only reference frame that could see it and then measure and calculate it as having happened after today would be one travelling faster than c relative to us.