The anarthrous theos is applied to Jesus and the Father in the greek scriptures, the New World Translation does not call the Father 'a god'.
Putting aside the inconsistency the Watchtower has in their book a separate being who is clearly identified as 'a god'.
And you are now stuck with that its in print.
By manipulating the text in an attempt to mask the deity of Christ, the Jehovah Witnesses have created the infamous 'a god' who is not 'like a god' nor is Jesus a false god, but 'a god'.
Hence the creation of a subordinate mighty god in the New World Translation, a functional polytheism from the perspective of the monotheistic Christian religion.
The definite article if present in John 1;1 it would not teach Christianity
It would be a verse that would support Sabellianism another heresy that actually predates the Arian heresy of the 4th century that most closely aligns with the modern day Jehovah Witnesses beliefs.
The position of the non existent article (if it was present) would mean anything that is the Father could be directly interchanged with the Word. It would be a statement of a Sabellian Godhead, which it clearly is not because of the anarthrous use of theos. John brilliantly wove a sublime verse by inspiration of the Holy Ghost.
Isaiah 43
“You are my witnesses,” declares the LORD, “and my servant whom I have chosen, that you may know and believe me and understand that I am he. Before me no god was formed, nor shall there be any after me.The Watch Tower bible and Tract Society says hang on Isaiah you have not read our New World Translation.
John 1 NWT
1 In the beginning was the Word,+ and the Word was with God,+ and the Word was a god.
https://www.jw.org/en/library/bible/nwt/books/john/1/.
