Thanks for your feedback. I appreciate that you are willing to bring these up.
As far as your point about "the Authority" being more vague and possibly confusing than "Governing Authority/Agency," I agree. It is. But I think you have to give the readers some amount of credit. Much more is spoken of about the Authority's state, aims and abilities through the dialogue, than its name. Since all of this info will be divulged through dialogue anyway, I'm willing to sacrifice a bit of clarity for the sake of the reasons I listed previously.
Succinctness is something that I occasionally find myself striving for when dealing with nouns and proper names in Blame. I think that in order to preserve the tone of the dialogue, care has to be taken to ensure that it retains its hardboiled nature. If I start throwing around too much text or keep using really longwinded translated proper names, it's quickly going to turn from a clipped, terse noir-ish sci-fi to pure hokey schlock. So I try to come up with names that are practical and sound like they would be quicker and more likely for the inhabitants of the world of Blame to use. I can't always stick to one strict guideline when translating because if you do that it is inevitable that the translation will suffer in some other area because of it. So it's kind of a give-and-take situation. As an anecdote contrary to my point about simpler names, consider what I feel is one of Nihei's few bits of cracked humor to escape into Blame: the GBE (Graviton Beam Emitter). The Japanese word is an incredible tongue-twister: Juuryokushihoushasenshashutsusouchi. Say that five times fast, and then notice in the Japanese text that there is no given abbreviation for it, and every time it is mentioned the entire name is used. Even when say, Cibo drops the gun during a fight, instead of saying "Oh, I dropped the gun..." she says "Oh, I dropped the Juuryokushihoushasenshashutsusouchi." Common sense would dictate that in such a situation you wouldn't waste 4-5 extra seconds attempting to work that one off your tongue, but she does it anyway...
I'm not sure where you picked up the idea that there are multiple entities behind the Authority. As far as I can tell there is no specific mention of either singularity or plurality in the Japanese text, so it's somewhat irrelevant. My point about the singularity of the name "Authority" was in contrast to plural names that others have used, i.e. Governers. If I were to have used "Governing Agency" you could apply the same reasoning.
And I think we can both agree, the Warren Ellis comment has no relevance to this discussion
EDIT: fleshed out my point a bit