Two events are considered simultaneous when an observer "sees" them at the same time at his clock. But when you see 2 events at the same time, it does not prove that they happened at the same date. Even if information propagate at light speed, the position of the observer wrt the events is overriding. When he moves during the translation of the informations, the simultaneity will not be the same. Let's try to define with some examples the notion of simultatneity or rather that of cotemporality.