The book consists of segments from multiple variations of the time stream.
Each "chapter" is from a slightly different version of reality, which explains details like the about-face of Green Taylor Simms's notes from "Let's talk about time traveling and spoilery stuff" to "Anyone who says you can time travel and do spoilery stuff is a whackjob", and the absence of Echo Lawrence from Chapter 42's list of contributors.
Echo was killed by the fire that Green Taylor Sims set at that gas station
She lived long enough for the police to question her about what happened, but she died soon afterword. The transcript of that interview became Echo's final contributions to the book.