Any of the books counts as a grimoire. The lectures of Teclis, the classical tome of hidden knowledge, the Magos's spellbook, or the writings of questionable sanity... which one you choose to follow may have additional consequences? The safe choice of course is the lectures or the classical tome. The classical tome has the secrets of one of the lores hidden in it. Once you pick a lore, from an RP perspective, it means you have uncovered the hidden meaning within the text.