I commute between Leeds and Doncaster on East Coast with a 5-Zone Metro Card and a season ticket between South Elmsall and Doncaster, The train doesn't stop at South Elmsall.
Most guards never had a problem with this combination, but last October a guard told me it wasn't a valid combination. I made a complaint to EC Customer Relations, quoting NRCoC Condition 19, but they refused to back down so I took it to Customer Focus. Eventually (last Friday) East Coast informed me through Customer Focus that it IS a valid ticket combination for this journey, and that they had informed all relevant staff.
The reason I gave them that it was valid, and the reason they finally conceded it was valid was 19c, that my Metro Card is not a season ticket (it was issued on behalf of WYPTE), and the other is a season ticket, so the train does not have to stop at a particular station.