I think they get away with passing off new light - because most JW don't even read or study most wt literature - they depend on the one who has.
I personally was not aware of many of their teachings, until I started reading every bit of wt literature I could get my hands on. And I started reading because I thought I was helping my spiritual weakness and depression -- and after my study of their literature, I was amazed at what we had been fooled into believing. And when I say study, this meant looking up the information they referenced in the footnotes and looking up all the scriptures. After doing this I realized I had been fooled. BTW, the only reason I had enough time to do this extensive research was because I was put on disability for depression (if I was working and keeping up with my household, I would never had found the time to do this). As with the JW being able to do extensive research, it is very hard for them with the 5 meetings the field service, their jobs and family.
So the WTBS will get away with practically anything they want to pass on - as long as the JW don't take the time to read and study their so-called TRUTH. And believe me, they will find a new twist to encourage the JW to get out their with a urgency to spread their message. If you have read the latest watchtower study articles, you can see the message.
Happy to be Free (Me)