Republication
Many commercially successful books have been republished, either by their original imprints or by other imprints. This explains why if you look up a popular book title at a large bookseller such as Amazon or a large library catalog such as WorldCat, you often find an array of different copyright years, publishers, editions, formats (hardcover, softcover, trade, mass market), and so forth. The exact distinctions between "reprinting" and "republishing" and on whether a republishing is or is not a "different edition" are not policed by any universal authority, so the meaning of the terms used in any instance cannot be known at first glance.
Read more about this topic: Edition (book)