Edgar Rice Burroughs, Why

Today in adventures in library cataloging: thanks to the big honkin' donations, we have big stacks of "replace battered old library paperback with shiny new hardback donation," and I decided to go through one of them. Early in the stack was Edgar Rice Burroughs's The Moon Men . There was only one problem: the paperback and the hardback, though identically titled and authored, weren't the same book…