You're research skills are commendable, Mel. I guess that's why you do what you do!
I have no doubt, once I had it in hand, that it's authentic, whatever it is. I know that sounds contradictory, but it just has the look and feel of an authentic, non-commercial, non-bootleg poster. Plus, how the hell could it be a bootleg of something that was never produced? Anyway, I don't know that I'd call it a unicorn, but it's definitely not common.