Indeed.It is rather bad though, as it forms part of the contract between the passenger and the railway.
nationalrail.co.uk doesn't allow me to enter more than one "via" points (well, it does but it shows itineraries matching only one of the via points), making me difficult to generate the itineraries I want.If you want to check a route is Permitted (rather than just to find out what the list of permitted routes is) if you get an itinerary on a single ticket via nationalrail.co.uk using your relevant via points then that is definitive.