Thats what started me waking years ago. Using the societies own publications and personal study I realized that spattering jehovah throughout the NT was completely unfounded. Then the more I dug... the rest is history.
You can look up their justification and research it well. Its pretty weak.
If memory serves me (and its been a while sense I cared) the best argument they have is quotes in the NT that are taken from the OT that would have had the "divine name". But that really doesn't answer was it really there in the first place. Think about the whole god damned NT... first of all, nothing about the supposed jesus was written until decades (nearly a century) after his death. Of those, no originals exist whatsoever... the more you dig you see the giant gaps in the book and the only thing that can fill them at the end of the day is huge amounts of blind/unfounded faith. When I realized that, things unraveled. I was lazy and never challenged much but just assumed the witnesses were the most scholarly well studied n the bible... NOT. They are just as guilty as any other religion of making it say what they want it to.
The Bible is like a prisoner... the more you torture it, its going to tell you what you want to hear.