J.L. Bell recently wrote about Glinda's Great Book of Records, and I don't think I ever did a proper entry on this magical item, so I might as well say a bit about it now.
The Book, which is sometimes said to record everything that happens in the world, is first introduced in The Emerald City of Oz. Glinda tells Ozma and her companions, "As soon as an event takes place, anywhere in the world, it is immediately found printed in my Magic Book. So when I read its pages I am well informed."
The remarks made by Ozma and Dorothy suggest that they hadn't heard of this book any more than the readers had. So did she only obtain it shortly before that, or just prefer to keep it hidden? Either explanation is possible.
In Land, Glinda mentions a book that tells all about what the Wizard of Oz did while in the country, but credits the information to her spies rather than magic (not that the spies couldn't have been magical). Is this Glinda talking about the Book of Records without revealing its true extent, or is this other book a precursor to the more famous one? The Sorceress tends to reveal so little that we'll probably never know.
Exactly how the Book of Records works is never clear, which I suppose is often the case with magic. I believe it was Melody Grandy in Zim Greenleaf who suggested the tome might have some kind of consciousness. I think I've seen the volume credited to both Lurline and Tititi-Hoochoo, two of the most powerful known beings in the Ozian world. Glinda also might have made it herself, but if so I doubt it's a feat she could easily recreate.
How much does the book actually cover? Despite the mentions that it records everything in the world, I would say this would have to be an exaggeration of sorts. It does, however, record much more information than anyone could use, and often in cryptic passages. In Tik-Tok, we're told that "[t]he smallest things and the biggest things are all recorded in this book. If a child stamps its foot in anger, Glinda reads about it; if a city burns down, Glinda finds the fact noted in her book." The book might well include some references to children stamping their feet, but I doubt EVERY time a child does this would be recorded.
My take would be that the tome is selective in some ways, but that not even Glinda can understand what system it uses to determine what news is worthwhile. In Kabumpo, it's revealed that news about Oz appears in red, which would presumably help Glinda find information relevant to her own nation. And in Magic, Ruggedo claims that the Record Book doesn't record the doings of animals, although this is contradicted in both Rinktink and Cowardly Lion, at least.