Board Thread:Questions and Answers/@comment-36649908-20181201214052/@comment-36649908-20181204055234

Sourcedartonline wrote: Reki Kawahara originally wrote SAO for a novel contest. He exceeded the page limits and didn't submit it. Instead he kept writing it and putting it on his website. When he won the contest with Accel world years later the publisher decided to publish both Sword art online and Accel world. The original web content was removed and published as actual novels.

The first few novels are largely the same as the web novel bar a few major exceptions like Asuna killing Kuradeel. After volume 5 the novels became full rewrites. Well I don't know about any of the other changes, but I think it was a good idea to change this part.