- You may be looking for the novel that features this fictional book.
The Book of the War was an encyclopedia-style primer for the War in Heaven, published 50 years into the conflict. Its authors and audience are never made explicit, but there are hints that it was written by brainwashed agents of the Great Houses (PROSE: The Book of the War) as a briefing (PROSE: Pre-narrative Briefings) for a human or posthuman audience. (PROSE: The Book of the War)
Reliability
The Book's entry on the enemy referenced several relevant entries that had apparently been retro-erased from the text. These were the Churchill Index, Immaculata Formosii, the Gods of the Ainu, "Miss Hiroshima", Mohandassa, Sixth Wave Defections, the S'tanim, and Violent Unknown Events. The Book noted that information related to Violent Unknown Events tended to corrupt or vanish. (PROSE: The Book of the War)
Like the orientation material that the Uptime Guard handed to visitors to the City of the Saved, (PROSE: Of the City of the Saved...) The Book incorrectly referred to the City's population as numbering in the septillions. (PROSE: The Book of the War) In reality, the census of AF 291 reported a population more than a hundred billion times that number, though the census results were not made available to outside researchers, and all data exports from the City were frozen later that year. (PROSE: Of the City of the Saved...) Several more of The Book of the War's statements about the City of the Saved were inaccurate, including the non-resurrection of culturally-human artificial intelligences and the dating of the Timebeast Assault. (PROSE: The Book of the War, Of the City of the Saved...)
Several of The Book of the War's statements concerning biodata and the Yssgaroth were old-fashioned and unjustified by the evidence. (PROSE: The Cosmology of the Spiral Politic)
Michael Simpson referred to The Book of the War as a briefing document created by the Great Houses. (PROSE: Pre-narrative Briefings)
Additionally, during at least one reading of the book, the Shift rewrote the reader's perception of the book multiple times to explain its own life story, and the entry on "You" Diversions arguably housed an example of its subject. (PROSE: The Book of the War)
Behind the scenes
The Book of the War was the fictional book-within-a-book contained in the Faction Paradox book of the same name.