There are Hebrew translations of the original Greek that use YHWH at 1 Cor 12:3?! I was not aware of that...
Why is the New World Translation inaccurate/not reliable?
First thing, there were no demonstrable translators working on it, so it would not properly be a translation. It is a rendering.
Then there is the matter of the renderers loving to use 5 syllables when one would do, supposedly because they loved to produce a lot of output. This make something like "grace" become "undeserved kindnesss" while "believe" becomes "exercise faith". This practice makes the narrative flow become ham handed without making the meaning any more clear.