I do find it weird that the last time the book was studied, it was with an addendum booklet of corrections "new light".
I wasn't in the org at that time, but I imagine I would've found that strange. It seems like an admission you're studying out-of-date material.
I don't know any other time in (relatively) recent years that was done, and of course now everything's electronic, the org will just quietly update the publication online and it will be pushed out to devices in the next update, so noone would be any the wiser unless they were paying "more than the usual" attention (with those in the congregation rarely are, or at least will rarely admit to!)
It was odd enough when the org went through a few years (in the mid-2010s I think) of constantly changing the songs and produced two different songbooks in quick succession. As if they couldn't make up their mind what the 'standard' music and songs should be, after having the same songbook for about 20 years. I wonder if there were changes and differences of opinion happening at the time among the GB and/or in the music/audio department?