Does it matter if YHWH was in the LXX? Isn't the question was it in the NT?
If the divine name was in the LXX and not in any NT manuscripts this only strengthens the idea that Jesus and YHWH are the same and the NT authors used the new name Jesus along with the title of Lord to speak of him.
I have seen that some of the J references that the WTS cites use the tetragrammaton in verses applied to Jesus.