An infamous (and common) editing error in White Wolf products, Page XX is a placeholder reference. During the creation of a book, page counts change and sections get moved around. When a passage calls for a reference to elsewhere in the book, "Page XX" is used with the intention that the final edit will catch these and be properly referenced. Far too often, these have slipped past the editors and ended up in the final proofs.
In 1st edition Werewolf: The Apocalypse, Page XX references were so common that the first edition Clanbook: Malkavian included an actual page numbered XX, with the title "because you kept asking for it".
Recently however PageXX has taken a sinister turn and been co-opted by Werenarwhals who are to blame for everything with their deranged love of cowboys