The thorny question of the Divine name as derived from YHWH, being in the New Testament has been debated long and hard on here, and throughout the Academic world where Scholars have an interest in the matter.
We cannot know what was in the Autograph Copies of the N.T Gospels, letters and Writings, because we have no manuscripts even close in time to the original autographs.
J.W Org claims to stick closely to MS evidence, favouring the oldest available as being more accurate, which is in itself debatable, but whatever, they are therefore being disingenuous in inserting "Jehovah" where they cannot find it in N.T manuscripts that we have, i.e nowhere. They have NO manuscript support for what they have done.
I am aware of all the arguments in support of the view, a mere opinion, that the divine name in some form did appear in the Autograph copies of the N.T. I have no firm conclusion either way, but either you follow the sensible method of only including in your Bible what you actually find in the extant MS, or you produce an Amplified Paraphrase version, based upon your own Theology and Christology, which is what the NWT is.