Invenire Duplici

Invenire Duplici - the finding copies spell. Alerts caster to location of copies or duplicates of the target of the spell. Harry ponders this wondering why this would be in a book for dark magic. After sometime he sees the some dark uses for this spell and comes to the conclusion if he uses this spell on this book he could destroy all other copies of this book so he would be the only one with the knowledge of these extremely dark magic spells. Does he track down all other copies of the book or does he find another spell to learn?