What purpose is served by the quote? Is the distraction of quoting from a "confidential" publication worth that distraction?
There's not much in the Flock or Shepherding books which is unique to those publications, so it may make sense to quote from a more accessible publication instead. I'd guess the main reason a person here wants to quote from the Shepherding book is to show that their local elders did or didn't do something they should or shouldn't have.
I'd guess a typical Witness will concede that individual elders are imperfect and at times foolish, even without rubbing his nose into the "proof".