If it isn't in print, it isn't so.
That's so 2015
The current litmus test is: If it is stated in a JW Broadcast video, it is the gospel truth*
* Until superseded by a later video.
Seriously - their video department is now the leading proclaimer of "new light".
I expect their November "monthly broadcast", available the first Monday in November, will break this newsflash by showing the AGM talk it was announced in.
The latest "Study edition" of the Watchtower available as of now (10/10/18) is January 2019. So I would expect the February or March 2019 edition to have a "Questions [made up by us but let's call it] From Readers" confirming this new light.