Dark Knight - the novel

Ok hear me out before you go "waaaat?" so I love the movie. And I've seen it a million times. But as we all know a movie is never the replica of the book and a book is never the replica of the movie (I challenge you to stay awake while reading LORT).
So...I checked out The Dark Knight. Its a novel written by Dennis O'Neil, and despite the line on the cover that says "based on the Warner Bros. Pictures film" the way the book is written, it looks like it came out first...I think...whatever.
So the question is why read the book when you've watched the movie so many times? Well I was kind of hoping it would be the sequel to the other Batman novel I mentioned earlier, Knightfall. But after reading the first three pages I don't think so. The books starts of with Bruce Wayne dreaming of how he killed Ra's al-Ghul, which basically is the end of Batman Begins. So now I'm super confused and stuck with the wrong book.
But God bless Wikipedia. Apparently Dennis O'Neil wrote them out of order, Knightfall in 1994, Batman Begins in 2005, and Dark Knight in 2008. Whereas the Knightfall story arc occurs during the tenth or eleventh year of Batman's career, while Batman Begins is how it all started, and Dark Knight is what follows. So what I'm holding my hands is a super-super-sequel.
But that's cool, I can't put the book down anyways. Within a few minutes of starting it, I'm totally emmersed in it and O'Neil's brilliant writing bring Gotham to life.
I think I'm gonna go ahead and buy all three books.
But what happened between year one, year two, and year ten/eleven?