It may have been less about the use of non-conference-approved literature, hp, than about "primary purpose"--AA's Big Book is the AA program of recovery. So use of that program's BB might have just seemed too much of a deviation from "primary purpose." The local "governing" bodies are but trusted servants, chosen by the groups in the area, and they are the ones who make the call on stuff like this.
My point really was that it's largely up to each group how they run their meetings. There's actually an awful lot of variations, sometimes from one part of the country to another.