Interesting info on IT. "The Collector.com" Broke down the printing of IT. I do have a true 1st/1st. 400,000 of these were made. Even though some of the other printings were fewer (still all 1st ed), the collector said that the 1st/1st is more desirable became it came out first. Sort of like my Salems' Lot being less desirable, even though there may be less because it came out later. I doubt it makes it more valuable, I am just glad I have a real first ed.
For more info on this including the other printing amounts you can go to Tom's website, IT section:
http://www.stephenkingcollector.com/1st/it.html
It breaks down everything very well.