I think this is one of those behind the scenes directives through a letter to the BOE. Supposedly the letter to the elders from the WTS says that it is up to the BOE to make the call, depending on how it is perceived in the congregation, would some of the rank and file be "stumbled" by it. Elders and regular pioneers are held up to a higher standard (supposedly) than the rest of the congregation. But then through the CO and/or DO this can be verbally strengthened. If you write the WTS, they might just put it back on the BOE as being responsible for the decision.
Did you know that the elders have an index to help them locate BOE letters? That they are not all supposed to have an individual copy of each letter but a central locked file in the KH is supposed to be maintained? (Yes, some POs keep them in their home...naughty, naughty...and some do make personal copies, double naughty naughty). I wonder how many there are now on file? That is why the Elders Handbook is good to a point but it is references to those letters and verbal directives from the COs that get penciled in that can change the policy behind the scenes.
The WTS is trying to tighten down on the congregations and if the elders and pioneers don't obey, do you think the rank and file will? "Why can't I do it, Brother Secretary does, and he's an elder."
Yes, there is a real life WTS Talmud out there, folks, hidden from the rank and file. But that is how a cult operates with unwritten rules.