Is a unicorn still a unicorn if you are the only person who wants a poster?
As many know, I am a collector of Sheryl Crow memorabilia and there has only been one instance of being able to cross that over with movie posters. In 2004, Regal Cinemas had one of their special "One Night Only" events in 25 theaters and played Sheryl's C'mon America concert. I was able to get the single poster from both the Nashville and Knoxville, TN locations and spoke to fans who saw the film in 3 other locations that told me they did not even see a physical poster at the theater.
Maybe those locations got them and were not displayed? Not sure. But I have never seen one on ebay (and have it as a saved search in a few formats), Bruce has never auctioned one, and I've never seen a copy elsewhere. Were only 25 made for the individual theaters? No Idea.
But I also don't know if anyone else cares or even would desire a copy. So is it still a unicorn?
Nope. Said it earlier. The poster in my avatar is the only known example. Probably couldn't get more than $200 for it. A poster needs to have 'buzz' and be wanted by a lot of people. It also needs to be difficult to obtain.
That said, I see a lot of stuff being called unicorns that are too available. Good examples are Revenge of the Jedi and the Why so Serious Batman. People call them unicorns even though they are up for auction monthly. I think it is a matter of sellers successfully generating buzz to raise prices.