The abilities that transform a Werewolf back and forth look at the entire previous turn, even if the Werewolf with that ability wasn't on the battlefield for some or all of that turn.
8 Apr 2016
To trigger the Werewolf's back face's transform ability, a single player must have cast two or more spells during the previous turn. If multiple players each cast just one spell during the previous turn, the ability won't trigger.