Where are the NPC mages’ spellbooks in the Lost Mine of Phandelver adventure?

In Lost Mine of Phandelver, the party comes across (and presumably defeats) multiple mages. These are not specifically described as Wizards, but their spellcasting is Intelligence-based, and they know spells from the Wizard spell list, so it sounds to me like they are Wizards. (If it quacks like a duck…)

Wizards, in D&D5e, use spellbooks. (See the “Spellbook” sub-section in the description of the Wizard class, p. 114 in the PHB.)

However, the Lost Mine of Phandelver material nowhere mentions the mages’ spellbooks.

Should my party be able to loot spellbooks? Or are these BBEGs actually non-spellbook-carrying casters? Or am I overlooking something?