...But it does contain discrepancies.
That, I believe, is the point.
This is a very clever book indeed. I'm sure you know that it is about young boys and the violence that these "monsters" (it's OK, I can say that, I used to be one) get up to, either for real or in their minds.
Litt's character development is so convincing, that by about half way through, you are terrified what one particular boy may do every time he appears on the page.
But where this book is particularly clever is the way the writer confuses you with the narration. Who is narrating this bit? Isn't that slightly different from the way that was described over there? Who was narrating that bit anyway?
You'll keep thinking about the end and what really happened for months after finishing it.