Note: Literary critics have, throughout the ages, argued both for and against the inclusion of prologues in large works. On the one hand, anything that is truly part of the story might just as well be considered its first chapter. On the other, some sequences of narrative exist solely to provide context, and may in that light be considered to not be part of the story. 

The argument becomes more nuanced when the prologues are placed before a story which is itself a "middle book" in a larger story. Those nuances vanish, middle-book-status notwithstanding, with regard to the inclusion of multiple prologues. For centuries the critics have shaken their heads, asking if there mightn't have been a better way to tell the story. 

Addendum: Literary critics defer to paleontologists with regard to whether or not Earth's dinosaurs had feathers, or telescopes. Paleontologists, with their tiny, clouded sliver of a window into that ancient world, get a lot of things wrong—notably, they fail to blame the disappearance of dinosaurs on passing aliens.