Jack: "We don't have time to sort out everybody's God."
Charlie: "Really? Last I heard we were positively made of time."
So now we know that some variant of The Others have been on The Island at least fifty years prior to the crash of Oceanic 815. We have reason to presume they have been on The Island even further back than that, but fifty years ago was when The Others first got wind that John Locke was going to eventually visit The Island and even become Their Leader. Now we know why some of The Others have been anticipating John's arrival; essentially because John visited them and told them he was coming, and that Jacob sent him. Talk about prophecy fulfilling itself! So this means the group of people we erroneously refer to as The Others have had over half a century of time to plan for the arrival of Oceanic 815. Here's the kicker: they've not only had enough time to plan for it, but they've had more than enough time to orchestrate it. We now have reason to believe that everything that led up to The Crash could have been manipulated by multiple agents of temporal change. From Jack's father 'dying' to Hurley's lottery winnings - all of it.
It now is not about what was destined to happen, but what had been destined to happen versus what was manipulated into happening so that destiny could change. There's talk of "rules" regarding time travel, but who made these rules? There's no rules. There's human beings making observations and thinking there must be rules but there's no actual rules. Desmond changed his own past so that he could be with Penny. Maybe the nosebleeds happen when you are not successful at improving your own past. Maybe the nosebleeds happen when you fail to change destiny.
Let's go back a moment to the episode "The Constant." Desmond meets Faraday, who is running a mouse he dubs Eloise through a complex maze. He says he never trained her. That he's going to train her later. He induces her with radiation, which we're told is supposed to move her future consciousness into her present body, so that the lab rat of the future can do the maze of the present, even though the present mouse's body has never learned the maze. This part of the experiment is a success. Soon after this, Desmond has a blackout (where essentially the same thing happens to him), and when he comes to (back), we learn that Faraday has spent the hour or so working out stuff on his chalkboard. Desmond also observes that lab rat Eloise is dead. Why is that? Well, it's not made plain to us, but since Faraday's so self-involved and neglectful, it's apparent to me that he never got around to teaching the lab rat how to run that maze, so when the present lab rat's brain attempted to catch up with its future brain, the temporal paradox of not knowing what it was supposed to know to run that maze caused its brain to turn to mush. So again, it's not that the nosebleeds mean you're breaking the rules. The nosebleeds mean you are failing to meet in your present the changes you have already caused to the timeline by your temporal hopping.