An author writes a trilogy. The third book is kind of a letdown. So a couple years later, the author comes out with a fourth book in the same trilogy, which acts as a new third book and completely replaces the original third book. Thing is, it’s totally different, even though it uses all the same setup from the first two books. Seriously, it’s amazing how well everything fits. You honestly can’t tell that the first two books weren’t written to be followed by the fourth book.
The fourth book is very popular, and lauded as the proper ending for the trilogy. That’s because it is a much better book than the third book. When the trilogy goes to mass market paperback, the four books get a box set. The standard accepted reading order is, one, two, four, then three if you feel like it, but you don’t need to. So the spines on the box set, the third book’s spine is the cleanest and least marked on most people’s sets, ’cause it gets read the least. How about that?
The fourth book comes to be known as the preferred third book.
So, was it a stunt by the author to generate publicity, or was it an honest, “I can do better, dammit” kind of thing?