Mark Lewisohn adds:

I'm meant to be producing 250,000 words for each of the three volumes, but, as soon as I began writing the first, I knew it would probably sail by its limit. I decided to carry on writing what I felt the story could deliver and take it where I felt it needed to go ... and when finally I finished, three years later, I'd written 780,000. 

To their great credit, Little, Brown (my UK publisher: round of applause genuinely deserved) said they wanted to issue the whole thing, all 780,000 words, as a premium-edition item. However, I still had to create a mainstream book (which we've called the trade edition), because a 1700-page tome j-u-s-t might deter the casual buyer. I spent three further months picking apart the full version's intricately-woven tapestry, reducing the word-count and then stitching it back together to leave no holes. Everything necessary is still present but what’s gone is even more colour and layers of depth and perception.

This is how we've ended up with two different products: the 960-page book (October 2013) and the 1728-page monster (November 2013). It's everything I wrote, and I'm very proud of it. More to the point, I'm happy with both books.