It's amazing to me when I see how much can change from an original printing of a book to a reprint, to the next reprint, and so on! I came across a brilliant example yesterday...
Now, I know this picture is small (I'll try to actually upload my own pic of the book I have at home soon), but you should be able to see that there is an actual half-clothed woman and centaur in a fantasyscape on the original cover of Goddess by Mistake by P.C. Cast.
Recently, with the amazing popularity of the House of Night series by P.C. Cast and her daughter, Kristin Cast, this previous series set in Partholon has been reissued along with two brand-new Partholon books targeted specifically to teens instead of adults. Attempting to push the books with a whole new attitude, the publishers changed the titles from Goddess by... to Divine by... and gave the covers a whole new look. Here is the new cover for Divine by Mistake.
What an amazing difference! If you didn't do your research, you might not even know these were the same book at all...but, very much more appealing to today's teens.