JW's have a strange attitude about this, no surprise there then. The attitude is both inconsistent, and hypocritical, as said above, their inserting "jehovah" with no textual authority for example, and it comes from a position of ignorance.
A number of early MS do not have this section because the page is missing, not because the words were never there. A number of early manuscripts that the WT relies on also have bits missing that the WT pick up from elsewhere.
The Eastern Church Fathers established church readings from what they considered to be Canonical Scripture long before the earliest manuscripts we have, 4th century, were even written. They include this section to be read, on St Palagia's day actually. It is inconceivable that they would include this section had they any doubts as to its authenticity.
The WT, like many totalitarian fundamentalist sects, does not like the teaching found in these verses, so are glad to drop it.
The passage teaches to ignore the rules and regulations and prejudices of the religious leaders, with their misogyny and lack of love, it was inflammatory stuff in its day, and bothers high control groups like the WT with its message of "you decide what is right".
To me, the words have the ring of the teaching and example of the Historical Jesus.