The recent Aeromexico airplane crash in Mexico is a good reminder of the fact that "the first report is almost always wrong." I was watching NBC Nightly News when they came on with breaking news about the crash in Mexico. They reported 103 passengers and crew on board, and "the U.S. government says no Americans were on board."
Fast-forward to when we know more, and fortunately all 103 survived, and now it is reported that there were up to 65 Americans on board that flight.
Just a reminder to you reference developing situations, "Remember the first report is almost always wrong." Yes, activate — get people moving to the EOC but continue to gather situational information since the story may change as more information becomes known.