Board Thread:Questions and Answers/@comment-5105419-20131205130839/@comment-1173941-20151208213336

The author originally wrote SAO for a contest back in 2001. Volume 1 basically started on the 74th Floor, though it also had a flashback to the first day. Think: Episode 1, and 9-14 (minus the Yui parts). In essence, the main story starts at the very end of the game already, and you start at the tail-end of a romance you're told has been going on for a few months.

Everything else has been a collection of side-stories the author wrote afterwards, which is why the timeline has so many holes. When the web novel finally became a light novel, it didn't really fix anything in the Aincrad "arc", and instead expanded the other arcs a bit. The anime decided to put all the side-stories in chronological order. (Because the books sure as heck aren't)

That said, the author has gone back with a spin-off series, called "Sword Art Online: Progressive", which is probably what you're thinking about; an SAO that covers the events of every floor, one by one. But it's only gotten to floor 5 so far, and the anime only includes the first chapter (episdoe 2). MAYBE they'll go back an make a spin-off centered on Progressive. But it's not a certainty.