hi mary
I'm just trying to point out a rule of thumb which is "Lack of evidence is not evidence of lack" just because the earliest copies we have don't use the tetragramation it doesn't mean it never was there! and howard an obvious trinitarian by his letter backing the 'deity of christ' can still say he sees that from earliest copies it could have been there, means we have to recognise there was a chance it was.
I have heard people on this forum use the lack of tetragramation in new testament as a support for the jesus is God argument, which is really making a massive leap even if it wasn't even in original copies which we don't have.
Even so, it's still highly dubious the way the NWT took the liberty of inserting "Jehovah" into thousands of verses in the Christian Greek scriptures
in the Old testament YHWH is used 6800 time officially no one argues with that at all, God definately wanted us to know his name in the OT
Jehovah's witnesses have inserted Jehovah in the New Testament 237 times not thousands as you stated, it could have been thousands but on the whole they only placed it were OT scriptures are quoted from, they did add it with some none OT quoting scriptures but you'll have to decide for yourself if they were right to in those cases..