Why we don't review previews, and the rare joys of seeing a show twice

Datebook: At preshow curtain speeches, when a company leader takes the stage to welcome audiences, I usually feel excited. A show is about to start! This is what I live for! But before the Dec. 6 performance of 42nd Street Moon’s “Scrooge in Love,” co-Executive Director Daniel Thomas said something that made me feel fear and self-reproach. “Welcome to the final preview of ‘Scrooge in Love,’ ” he began. “Preview?” I whispered to my companion, blanching. “I’m not supposed to be here!”