> Changes should always be documented in NEWS.  NEWS.25 describes
> changes in Emacs 25.x for Emacs 26 and higher, so it's never relevant.

Thanks, I've added it to the "Changes in Emacs 26.1" section.
 
> Did you look into the Emacs manual, to see if it also needs an update?

I've updated the existing manual entry now as well.