Jason Scott, connoisseur of all things old-timey, knows (and loves) his gaming history. His Flickr gallery shows this. It also shows, remarkably, that he's got a copy of the lifetime sales figures of a bunch of Infocom games. Infocom being the developers of games like Zork and Hitchhiker's Guide To The Galaxy. It's fascinating stuff, especially when you consider that shifting 380,000 units of Zork between 1981 and 1986 is, relatively, shifting a lotta units.
Great Scott: Infocom's All-Time Sales Numbers Revealed [GameSetWatch]