TMoST was based on a lot of behind-the-scenes memos, notes, and discussions with the production staff. However, some of it may have been "Whitfield's" (Poe's) interpretation or distillation of the ideas. In any case, TMoST was the
Trek reference book in the early years of the show, so it's quite possible that it influenced the later decision in the movies to lock the time frame down as the 23rd century. Which would mean it was itself the original source.