[charlesatan]

With regards to the fix-up novels (i.e. Ender's Game), you don't count the original publication it was printed in (i.e. a magazine, an anthology), since the point of sale to that is the source (i.e. Asimov's magazine, Eclipse anthology, etc.). Edit: Unless the short story/novella/novelette was sold as a book, which didn't really happen often until now (with the proliferation of eBooks or special editions).

Multiple editions, however, is a valid point, and depending on the source, they tend to be counted as one (although individual best-seller lists like NY times or USA Today will usually just count one version of the same edition [i.e. hardcover] that includes reprints of the same edition [but not one by a different publisher]).