Today, I called him on it again in a different thread and this time he responded. Well, turns out he found the photo on the LA Public Library site, where it was fully identified. And who do we think was the identifier, uncredited? That's right, it was one of the many photos that I've been sent in hopes that I could ID them. When she sent me the Groucho photo, she knew it was an opening night, and she guessed at what word the three letters you could see on a poster were - unfortunately, the guess could not have been more wrong.
