I knew that Jehovah wasn't the actual name of God, but thought it was an improvement on the more vague LORD and therefore it was 'better'. But whilst I was waking up I did research and realised that Jehovah is a hybrid word. A mixture of two words (consonants of the latin version of the tetragrammaton plus the vowels of Adonai) thus making this a totally made up word!
It's also interesting that in the 60 odd years since the NWT was started, Bible Scholars and academics use 'Jehovah' less and less as Yahweh has gained ground as the more correct version of the tetragrammaton. And they quickly point out that even Yahweh is a best guess.
The penny really dropped when I was trying to think of how best to illustrate this to my mother (should it come up in conversation) and thought up this way of expressing the problem.
Lets say the exact translation of the name of God was unknown from an old language. The closest translation is Robert but an old version created by a catholic hundreds of years ago is William. Which name would one use to get 'closer' to God?
Of course one immediate problem is that God still hasn't made it clear what his name is in modern languages, but surely, at the very least, he would direct his people to use the closest one, Robert?
And there you have the problem in a nutshell for JW's. God has apparently directed his only people on earth to stop using one inaccurate version (LORD) and instead use another inaccurate version (Jehovah) whilst a more accurate version is already known (Yahweh). And the inaccurate version, Jehovah, is what he wants to be used as a witness to all the nations.
Madness!