Here's something to think about:
We know the name existed in the OT even though there are manuscripts with it removed and replaced with the Hebrew version of Lord. But the OT is a lot older than the NT. There was thus a lot more opportunity to thoroughly remove YHWH from the OT copies without leaving a trace . . . and yet we have OT manuscripts containing YHWH!
Is it reasonable to believe that copyists of the NT succeeded in thoroughly removing YHWH from the NT while failing to do the same for the much older OT? How likely is it that copyists would succeed in totally removing all occurrences of YHWH from all NT copies without so much as one surviving with YHWH? That seems highly improbable. It is far more reasonable to conclude that the name was never in the NT to begin with.
By the time of the NT's writing, it was already the culturally accepted norm to substitute YHWH with Lord. All of the Jewish culture was doing it and all the early christians who initially came from a Jewish background grew up doing it. Even the copies of the septuagint in use at that time had already replaced YHWH with kyrios - never mind the fact that there may have been a minority of copies with YHWH. It certainly was not the norm. So even the argument about NT writers quoting the OT where YHWH is mentioned, is flawed! Why? Because the NT writers were likely quoting from later copies of the septuagint which already had the name replaced with kyrios! It is only natural then, to expect that early Jewish christians - the writers of the NT - would continue the tradition they grew up knowing and practicing, in their NT writings. Remember too that it was considered blasphemous to use the name.
Why would christians go out of their way to use the name and bring persecution on themselves when the bible does not mandate the use of the name? Consider too that the majority of the books of the NT are letters that were read out loud at church meetings. Do you think the authors would write YHWH in them and have the reader at the church meeting accused of blasphemy by some unbelieving Jew who happened to be visiting the meeting?
I think the most logical and objective conclusion that one can arrive at in view of the total absence of any NT manuscripts with YHWH, is that the name was never in the NT to begin with. It is only because of theological bias - their over-fixation on the need to use "Jehovah" - that JWs want to believe that it must have been there. They cannot believe that early christians did not share their unhinged fixation on the name "Jehovah".