Gregg's name does not appear as an author on the Functional Manual. He does write a foreward, and in that he makes it very plain that he feels that students should start writing practice immediately rather than waiting until later in their study as Leslie has done in the Functional Manual. And then, as soon as Gregg dies, McGraw Hill publishes a simplified version of the system.
So the question has been on my mind all weekend. These two men worked with one another for years, and yet seem to have had fundamental differences of opinion. Are there any biographies which talk honestly about their relationship, working or personal? I have a feeling there's an interesting story here.