Imagine if you will a member of a religion wrote a letter to a locale specific group of fellow religious members. A group the size of a congregation. Later, all members of said religion get a hold of that letter an incorporate it as being God's own word.
Now we know how the Apostle Paul misogyny was incorporated into Christianity - a religion based on Paul's letters to congregation made up of followers of the teachings of Jesus. Jesus, who held no such teaching or belief as Paul.
The Watchtower's protectiveness of the Shepherding book borders on secret society behavior. Take for instance the direction that elders may only take the book to a male Jehovah's Witness bookbinder and that any work done on the book must be done under the direct supervision of the elder.
Why all the secrecy? Civil and possible criminal liability. Watchtower claims that all the content in the book may be found in their other publications. This is partially true. The difference is that the Shepherding book is not ambiguous as the rest of the a Watchtower's publications are. That is intentional so they don't paint themselves into a corner.
The Shepherding book is different. It is specific about the actual beliefs and practices condoned by the Watchtower. Watchtower policy on handling child abuse cases inside the congregation are a clear example of this. Other Watchtower publications will condemn child abuse and make statements like "Child abusers should be handed over to the authorities and not protected by the congregation." Whereas the Watchtower's actual written, but hidden policy, is to report the case to headquarters and wait for instructions.