I read a textbook writer course. What is prohibited: for example, do not tell you verbally up your book and then it typed with someone else.
Second: do not put your older studies in a volume.
Do you think they are true?
Well I do not think are true. If so, I would never have written my first book. Because I verbally up the text of the book and typed them the helpful women.
I don't practice in the machine writing, I would never have done if I have all 300 pages to describe the typewriting. Of course compared to the live speech to edit a lot, but anyway also have to edit a book.
And I plan a book will publish from my older studies. Why not? These studies one by one too short but putting together they add up to a book.
There is still a problem after that?
The point is not to jump to any gurus instructions. Do it the way it feels good to you then your readers will decide whether they like it or not?