If the official tutorial or manual is lacking, the normal procedure should be to improve it, not to write your own entire document.
Or, in today’s parlance: Submit a pull request before you fork the project or write a complete replacement for it.
These courses/books provide examples that may benefit people who are looking to get into Python/programming to solve a specific problem or to build something they've envisioned.
"Submit a pull request before.."
The unofficial documentation and related tutorials are exactly that, unofficial, they are not meant a replacements by any stretch of the imagination for the official documentation. Rather, these forks exist to speak to many different audiences and in some cases, speaking from personal experience, attempting to document and teach others is a very useful tool for personal edification regardless if it is a distraction from the "blessed" documentation.