Just read this on the cross-boundary travel section of the WYPTE website:
Sorry if this has been brought up previously, but how exactly can these three TOCs refuse to apply a ruling which I thought was in the National Conditions of Carriage?"Please note that on trains, fares may be combined only to and from a station at which your train makes a scheduled stop. Where a passenger holds two or more zonal tickets in combination or one is a rail season ticket and one is not, then the train does not need to call at the station where they change from one ticket to the other. Please note that these combinations of tickets do not apply to services operated by CrossCountry, East Midlands Trains or East Coast."