Is this so? If I'm sitting in the pub around the corner from the station with an Advance ticket, and I see that my train is an hour late so I stay for another drink, is it really true that I can't claim Delay Repay because there was an RRB I knew nothing about?
If an additional service runs (which could be an additional stop, which - as with buses - may not always appear on online systems) and is advertised to everyone at the station, but you chose not to be at the station, then generally speaking you could expect to find the claim rejected on the basis that a service was provided.
Certainly the historic situation - before a reliance on online information - would have been to stick around at the station if you wanted to minimise a delay, but these days there is an expectation of being able to see information remotely from the station, but I am not sure if there is a right to argue that you can exclusively rely on such information.
If you took all reasonable efforts to establish if an alternative option was available and if the train operator didn't provide any such information of any alternatives, except to passengers at the station, then you would have a reasonable grounds to dispute any such decision, but I am not sure that either party could definitively point to any particular rule that would indisputably settle such an argument either way.
), and so such journeys normally get covered by bus, particularly if it will be out for more than one round trip. However very rarely is this bus entered in the timetable systems so you'd only know about it by being at the station and seeing it sat outside.