I do not read Watchtower materials anymore, so I won't go look this up. BUT I believe your "copies of copies" thought from WTS is to explain how the Hebrew text was arrived at and it doesn't specifically mention the name "Jehovah" in the Greek text coming to them this way. For "Jehovah" in the Greek text, they say that a great apostasy occurred and we are supposed to forget that Jehovah protected or preserved the text long enough to assume the apostasy was successful enough to remove the name "Jehovah." Then the unnamed WT scholars simply compared the Greek texts to the Hebrew texts they were obviously referenced to and put "Jehovah" back into the Greek wherever they determined that it was in the Hebrew text according to the "copies of copies" idea.
If that doesn't make sense, remember who we are dealing with.