What's not clear from the study (at least skimming it) is if they always started the ball rolling with ground truth passages or if they chained outputs from the model until they got to the end of the book. I strongly suspect the latter would hopelessly corrupt relatively quickly.

It seems like this technique only works if you have a copy of the material to work off of, i.e. enter a ground truth passage, tell the model to continue it as long as it can, and then enter the next ground truth passage to continue in the next session.