You forget that she was the wildcard; only her. The assumption is that Quentin wussed out at the last minute all the 39 times prior and Alice drank the essence (the Beast indicated surprise at them getting "this far", meaning…they have before, maybe not every time, but some). So, Julia taking the knife clearly…

Yeah, for those people arguing the "Julia is evil" thing:
a) All she did is leave, essentially a bunch of people that hated her (and Quentin, who she clearly saw was unharmed)
b) PTSD is clearly going on (she has only the equivalent of a day of mentally comprehending her own rape)
c) All we saw is that she left; how long…

Well your other problem there (and solves your issue without temporal physics). Quentin was from the future and got teleported to Fillory's PAST (circa 1940s Fillory). He was freeing the writer of the book, who learned it from Quentin. She wouldn't produce the book until much, MUCH later, at which time Quentin…

But…that's the entire point of time travel; causation in temporal physics (if it was…real) gets potentially thrown out the window. Like River Song in Dr. Who getting named by her parents who, according to Dr. Who Confidential, picked Melody because of meeting….River Song.