I wouldn't read too much into changes on brfares.com, as they don't know why the train companies have made any of the changes they show.
I'd expect something on the Chiltern web site if they'd introduced cheaper fares on some routes, like you see on
TfW. Chiltern still have the "January Sale" promotion up on their home page (even though they say it's already finished), and there's nothing about these new fares.