So in GR, for a classical black hole, if A is approaching the event horizon, to an observer far away, let say B, B would never observe A crossing the event horizon as B would observe A's time slow down in the limit to 0 and A's length contract in the limit to 0. In fact, according to B, A never crossed the event horizon. But A in it's own reference frame crossed the event horizon. So then in this case, would A and B disagree on causality since both A and B completely disagree on what even happened? Then would that mean that causality is relative?