Karen Azenberg, a past president of the Stage Directors and Choreographers Society, stumbled on something peculiar before the union's 2015 move to new offices: a 52-year-old sealed envelope with a handwritten note attached. It was from Agnes de Mille, the groundbreaking choreographer of Oklahoma! and Rodeo. De Mille, a founding member of SDC, had sealed the envelope with gold wax before mailing it to the union and asking, in a separate note, that it not be opened. The reason? "It is the outline for a play, and I have no means of copyrighting…The material is eminently stealable."