Despite the fact he only needed to write 50,000 words for a companion book to his A Song of Ice and Fire series, George R. R. Martin reportedly wrote 250,000 words for the book.
Tower of the Hand blogger Pharout attended the ConQuesT 44 convention in Kansas City, recording the Game of Thrones author’s commentary during two panel discussions. According to Martin, he wrote this epic material for The World of Ice and Fire: The Official History of Westeros and The World of A Game of Thrones. Here’s more from Tower of the Hand:
The extras have been put in a file for a project they are now calling the “GRRM – arillion.” Way down the road. The premise of the “World” book is that it is a copy of a tome presented to Robert just after the Rebellion. The “article” he read was written by a Maester Glyndon. Glyndon distilled his work from three other accounts of the conquest: one from a septon, one from a Grand Maester, and one from “The Tales of Mushroom” a court fool. George actually wrote all three of these pieces as well.
Link via A Dribble of Ink