If I had the free time in November to devote to it, I wonder if I'd run into similar issues given the way I write. I backtrack and re-write all the time and even feel the need to add scenes several chapter back just to balance the story. I can see how that would be a detriment to the NaNoWriMo goal. I give serious props to the authors who can do it.
All the best to those participating and I hope some day to get it a try. Not sure what the result will be, but someday. Good luck all!