In this case, I tend to agree with the people who were involved in the printing of this particular poster, and the experts for the movie. Some people will not believe certain things unless there is a "smoking gun", so to speak.
It all comes down to what you want to believe in. My experience in this hobby when it comes to print runs is that no one knows for sure, lots of people assume things, people throw numbers left and right, dealers spread false information for the sake of upping the value of a given poster. Mel first started with a 250 print run, then if jumped to 500 (Kilian), it was sent to theaters still playing the movie, then it was only given to employees... Truthfully, I don't give a damn one way or the other. I personally don't believe it. My years in this hobby make me very suspicious of any kind of assumption. By the way, I own a lot of these supposedly rare posters, so it is against my own interest to not believe that I own this one of a kind poster, but I do. When I buy a French poster like Laura and I am told by 3 different collectors (and multiple dealers who have never seen it) that only 2 still exist in the world, mine and one in Japan, I want to believe it but it seems so ludicrous that I still feel there is a stash somewhere waiting to be discovered.
T