Take the example of "This Gun For Hire" one sheet. We know there have been 10 sales in the last 10 years from Heritage (7), Emovie (1), and Christie's (2).
By contrast, there have been 60 sales of "Forbidden Planet." Can we assume that there are roughly six times more extant FP posters?
There are probably 20-30-40x more Forbidden Planet one-sheets than This Gun For Hire.
In 1993, my partner went to a friend's house in Miami after he had returned from Cuba and among the loads of goodies he had, he laid out 17 never-used snow-white papered copies of Forbidden Planet.
I had only been part-time selling for a few years (we owned two comic-book stores at the time and that was our main thing) and was afraid this was going to crash the market on the title, so I mistakenly only bought five copies. The other 12 he sold in one lot to a very prominent NY dealer.
Later on when I was telling (more like warning) some of the other then-long time dealers about my purchase and what I had scene the response was more along the lines of "That's it?", with a prominent local dealer (Paper Chase) telling me about an exchange they had purchased a few years prior where they had ended up with over 40 copies of Forbidden Planet (all in various stages of use/non-use) and that was after the exchange had been selling off posters to collectors for over a decade.
I have found that there are generally five levels of rarity in posters
5. Post Star Wars.
That one movie really turned the hobby around. Dealers were buying rolls and rolls of this poster for years (literally) and it ramped up demand for all paper in general
4. 1960 - 1976.
It was around this time that some organized collecting started in earnest, some exchanges started selling material directly to collectors, and some dealers started speculating in "new" releases (James Bond, etc). I have a Film World catalog from 1967 that lists most James Bond and 50s sci-fi posters at $1-2 each already, and actually has some early Universal horror lobby sets priced at $75-100 per set (including Dracula). The most expensive item in the catalog is an original German set on Die Nibelungen for $250. So even back then the rarity of certain pieces was already established. (and Bruce if you are reading this, I loaned this to you and would like to get it back some day).
3. 1945 - 1959.
Post-war and most things can be found with a little effort, as the NSS basically stored everything until they couldn't use it anymore.
2. Post NSS, Wartime (1940-1945)
Wartime paper drives pulped tons of material made during this time (and earlier), but NSS kept enough stuff around to ensure they could supply posters to theaters
1. Pre-NSS, Pre-War (and then add pre-code for some more toughness).
For each studio, the dates will vary as to when they signed their contracts with NSS and the paper becomes more plentiful, but as a general rule pre-NSS material from each studio is drastically more difficult to find than post-NSS.
Of course there will always be exceptions to the above rules (Stashes of individual titles found somewhere, or particular titles pulped prematurely, etc.), but this gives a general guideline to how I see the rarity of most paper. Perhaps Bruce, Rich, or other longtime dealers can give their own thoughts.
