Do Jehovah's Witnesses think there is an important difference between saying 'Jehovah' and 'Yahweh'?

As the denomination's name implies, Jehovah's Witnesses place importance on the name Jehovah. Do they distinguish between Jehovah, Yahweh, the Tetragrammaton, and so on, or do they think these are all acceptable versions of God's name? Also, is there any emphasis placed on how to pronounce 'Jehovah', or is the pronunciation considered non-essential?