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Is it possible for Quirrell to have been in the DADA teacher for more a year? Could this be because he had Voldemort sticking out the back of his head?

marked as duplicate by Jason Baker, DJClayworth, Adamant harry-potter Oct 2 '16 at 3:23

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As per this question, Prof. Quirrel was previously the Muggle Studies teacher. This easily enough explains Percy's recognition of him. Whether or not he took Muggles Studies, a top-level student (and top level suck-up) like him would of course know of all the staff at Hogwarts.

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