@WooShell @oantolin I remembered this article giving a horrifying insight into the American textbook process. Especially the quote "The books are done and we still don't have an author! I must sign someone today!" (The 'author' probably wrote no more than the introduction.)

Found it again and oh wow, it's more than 20 years old. It was fresh in my memory.

Still, here's how things were done in 2004 and I can't imagine it's got any better.

"My assignment was to reduce a stack of pages 17 inches high, supplied by 40 writers, to a 3-inch stack that would sound as if it had all come from one source. The original text was just ore. A few of the original words survived, I suppose, but no whole sentences.

To avoid the unwelcome appearance of originality at this stage, editors send their writers voluminous guidelines. I am one of these writers, and this summer I wrote a ten-page story for a reading program. The guideline for the assignment, delivered to me in a three-ring binder, was 300 pages long."

https://www.edutopia.org/textbook-publishing-controversy