Leo, great work on this...
FWIW, I've had a sneaking suspicion that the WTBTS altered their translation in NWT to read "Faithful and DISCREET slave" (vs ALL the others, which use "faith and wise") as a result of the fall-out between Rutherford and Moyle, as if to insinuate that Moyle had betrayed his attorney/client confidentiality duty by being "indiscreet" about the Society's "private" matters (of course, Rutherford and Moyle were both lawyers; oh, the hubris of Rutherford to think that drinking at Bethel actually WAS the "master's business", LOL! In fact, Jesus' parable WARNED about the evil slave drinking with other servants, LOL!).
In the documents you presented, I found it very interesting to see Rutherford refer to Moyle's using "the very language of the evil servant class", which suggests that Moyle WAS considered as on par with the FDS, except instead being the evil servant! Rutherford seems to have decided to deflect the blame by making Moyle out as the bad guy, and not a whistleblower?
I'm just mentioning it, as that seems to be some compelling circumstantial evidence to suggest the fall-out between these two may have been a factor in the odd choice (eyebrow-raising?) of words for the NWT? Keep it in the back of your mind as you search, looking for anything that supports the hypothesis of a "personality-driven" (namely, Rutherford's) translation having been used. What a story THAT would make, if it had stronger evidence to support it....