But the 'error' predates these sources.
Scholars now understand that the spelling came from Christian translators in the 12th century, who conflated the vowel marks of Adonai (Lord) with the consonants of the Tetragrammaton to arrive at IEHOVAH which later became Jehovah – the point being the Christian scribes did not understand the text they were translating ... so in that sense, unfortunately, the Witnesses perpetuate a mistake which later, more accurate translations of the Hebrew Scriptures, sought to correct.
It's all there on the
wiki page.
One can argue the term is now the tradition of the Witnesses, and defend it on those grounds.
It's a two-edged sword – if you're gonna make a big deal out of 'cross' as a misinterpretation of the Greek
stauros, then buy the same token you're gonna have to acknowledge that Jehovah is a mistranslation of the Hebrew.