There were several versions of the Greek Septuagint. The texts located at the Dead Sea shows great variations. apart from the Isaiah scroll.
In its NT, the WTS does not limits its use of "Jehovah" (not the Tetragram) to places where the OT might have used the Tetragram. In places where the Greek text does include it, we see ancient Hebrew characters in a Greek text. These characters were so ancient at the time of the DSS community, that they were no longer in use.
I have a copy of a recent letter from Professor Howard in which he once again complains of the WTS's misuse of his work. He, of course, limited his work on Matthew's gospel, based on a middle age Hebrew text which used "H" to represent "Hashem" - The Name.
Doug