Board Thread:False Info and Speculative Discussion/@comment-24782789-20140621151955/@comment-6383956-20140624112650

What if the circumstances are more specific than that -- like it could be any combination of the three things that were true of Derek's blood rather than just one. (I would imagine that, since the Alpha spark transfers, it might be that it needs to be the blood of the now-Alpha who killed you. So, like, if Derek had done that healing thing and lost his Alpha status, Peter couldn't be resurrected. Just thinking out loud here, though!)

As for how Peter knew.... have we not figured out by now that Peter (and several other characters) are sitting in the writers room? Because they know things they could never possibly know all of the time. :P