Two things to mention about the JW trinity teaching. Firstly, they cannot decide when the trinity teaching started:
WHEN DID THE TRINITY DOCTRINE ORIGINATE?
4th CENTURY - w61 2/15 p. 104
'A "Holy Trinity" of three Gods in one God is also worshiped by most Catholic and Protestant sects, this having first been adopted as Catholic doctrine at the Nicene Council of A.D. 325.'
5th CENTURY - w69 7/15 p. 421
'Thus the Trinity was unknown to early churchmen. Actually it was some 400 years or more after the death of Christ that the concept of 'three persons in one God' was finally formulated by men and introduced into the church.'
2nd CENTURY - w78 5/15 p. 27
'The vast majority of the churches of Christendom still teach such doctrines as immortal soul, Trinity and others, which filtered into apostate Christianity from the second century C.E. from Greek philosophy.'
3rd CENTURY - w2000 6/1 p. 5
'But by the third century, certain influential clerics, enamored of the trinitarian teaching of pagan Greek philosopher Plato, began recasting God to fit the Trinitarian formula.'
Next, the JW teaching of the Trinity was first stated in a WT of 1882. This was before the JW's were chosen by Christ and before the GB came into being.
Basically, the WT organisation got more things right before their famous 1918/19 selection and appointing than they have done since.