Information regarding meeting in small groups was removed.
Watchtower's go-to scripture on meeting attendance is Heb 10:24, 25. In older NWTs that verse had several cross references listed (in the center column), some of which were removed in the revised NWT.
In the image below notice that in the previous NWT, after the expression "gathering of ourselves together," there is a reference to the center column which has 4 scriptures noted. Then in the rNWT the same verse, after the words "meeting together," there are only 2 scriptures noted - Mt 18:20 and Acts 20:8 have been removed from the cross references.
Mt 18:20 is the main one of interest in this post. It says...
"20 For where there are two or three gathered together in my name, there I am in their midst.”
I would be interested in hearing Watchtower's explanation for removing this reference. Of course the official explanation and the real reason are probably two different things. In reality it appears that Watchtower's concept of Organization is being violated by this verse. Can you imagine Watchtower allowing Witnesses to break off into small groups, as small as 2 or 3, to have meetings? Absolutely not. Watchtower organizes all the meetings of JWs and tells you where and when to meet. Even though Jehovah supports it, the Bible supports it, and Jesus Christ supports it, the Governing Body would never allow such a thing.
So, the cross reference to Mt 18:20 just haaad to go!
(I suspect Watchtower would say that verse was meant for remote locations where only small groups could be formed, even though I can't find anything to that effect in the scripture.)
(FYI, the other verse that was eliminated, Acts 20:8, tells of the young man Eutychus that fell asleep at a meeting (in vs 9) and fell out of a window. Maybe that reference was removed because it hits too close to home - Watchtower's meetings tend to be overly boring, putting people to sleep.)