The thing is what we know about the book is that the earliest picture they have shown is young Snow when she is about to touch the flower. Though we also know that Henry knows about Jiminy taking a long time to do the right thing so that means his story is in there. And we also know that the book is not completely right because it says that Hansel and Gretel’s father abandoned him when really he was kidnapped by Regina.
Also i think that they will for sure continue doing flashbacks in fairytale land. I just wonder how much they are going to use the book in the same way.