Generally speaking, Marty Greenberg printed 5,000 copies of a title, although as with every statement about Gnome there are exceptions. He printed so many because he used a large printer that was set up for large print runs. I worked with a printer like that once when I was business manager of the SFWA Bulletin. They wouldn’t bother doing a run smaller than 2500 copies even though I only needed 2000. Yet their price for 2500 was less than what other printers charged for the smaller amount. So every issue 500 extra copies arrived at my house and piled up in my basement. Greenberg had it even worse. It cost him money to bind the printed pages, so he bound only the minimum needed at first and then bound others when and if the first set sold out. The rest of the copies sat in his office, or a warehouse room next to it, or were all but held hostage by the printer, who kept piles of the unbound copies and charged him storage. When Greenberg needed those copies he had them bound with apparently whatever materials would cost him the least. These were usually boards – pressed cardboard – although there are cases in which a better cloth was used. At any rate, no pattern has ever been discovered for these variants, which are of all colors, some not part of any earthly rainbow. All of the variants, with the following exceptions, are of different board/cloth color combinations.
There are two known cover illustrations that are entirely different, for The Forgotten Planet and Travelers of Space. Foundation has two completely different rear covers. Foundation and Empire has three different numbers of books listed on the back cover, along with some minor changes elsewhere. It also has a second state front cover, printed only in blue and black. Men Against the Stars and Journey to Infinity have second state back covers. Methuselah’s Children gives the New York full address on the rear cover and back flap in the first state, and just “New York” on the rear cover with the Hicksville address on the rear flap in the second state. Tros of Samosthrace had its price raised from $4.50 on the first binding to $5.95 for the second. I. Robot, Cosmic Engineers, and Pattern for Conquest were reissued in trade paperback format. The Thirty-First of February had a special slipcovered edition for the hardback and was also in a trade paperback format. There may be many more small variations out there to be discovered.
NOTE: I’ve separated out a few titles for special mention under the menu header of Not In Currey. That’s because Currey states are normally the only ones ever given in dealer listings. The ones I know of are Earthman’s Burden, The Forgotten Planet, The Seedling Stars, and Two Sought Adventure. The Seedling Stars also has a variant dust jacket, with a gray spine instead of a green one.