Let me repeat myself... Because "Jehovah" is totally absent from both the Old Testament and the New Testament, it is evident it is not there. All you have is the tetragrammaton (four unpronounceable consonants in its stead) in the OT and 3 Hallelujahs (fragments of the name) in the NT.
<<Here is a place in the Hebrew Scriptures the name is used and written:https://www.biblegateway.com/passage/?search=Exodus+6%3A3&version=AKJV>>
Yes, the KJV actually employs the name Jehovah 4 times....but these are derived from adding vowels to the tetragrammaton. So again, Jehovah or Yahweh is not in the Hebrew scriptures.
Thus the KJV is guilty of adding to the word of God 4 times while the Watchtower is guilty of adding the name Jehovah close to 7000 times in the OT. But regardless...Jehovah is not there.
<<Knowing that, can you say for certain that the DN was not written at all in the original Greek writings?>>
Can you say for certain that it was? And if it was, why didn't God allow at least some ancient manuscripts to contain the name? And how then could anyone trust the scriptures If men can so thoroughly alter God's word.
It is evident then that God wanted another DN to have preeminence.