I have two opening night (gold cover) Playbills from the late 1950s of flop Broadway shows my mom was in. I guess those would be pretty rare, although I don't know how valuable they would be. Each show only ran a couple of weeks, but one of them was made into a movie a few years later. Still, not very well-known, I would imagine. It's kind of interesting to see the gold covers though (full gold, not just a seal).
I have a few older Playbills, but doubt that they are rare because the shows were pretty popular:
Hair (when Diane Keaton took over as Sheila)
Bells Are Ringing (OBC)
My Fair Lady (OBC)
The Most Happy Fella (OBC)
Also a few from flop shows that I saw in the '80s:
Smile
Into the Light
"Jaws is the Citizen Kane of movies."
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