 The final "Graduation" episode had already been shot when the  network ordered additional episodes. Tiffani Thiessen (qv) and  Elizabeth Berkley (qv) were attached to other projects by that  time, necessitating the creation of a replacement character Tori,  played by Leanna Creel (qv). The Tori episodes aired in the middle  of the other final season episodes to sidestep continuity problems  (though the disappearance and later reappearance of Kelly and  Jessie, as well as for Tori, went unexplained). 