I'm currently a Gold Card holder between Didcot Parkway and London Paddington so as a benefit of this I have been able to get my wife a Network Rail card for ^1.
My wife has used this Network Rail card between Didcot and Paddington on a number of occasions now to get 1/3 off the standard fare with no issues, however when she tried to use it yesterday to buy a ticket between Didcot and Oxford (at ~14:00) she was told that her Network Rail card couldn't be used and she ended up having to pay the full fare without getting the 1/3 discount. She obviously didn't know any better so just accepted it and paid the full fare.
I have checked the Network Railcard routes and the route between Didcot and Oxford is definitely shown as a valid route...
http://www.railcard.co.uk/clientfiles/files/map.pdfDoes anyone know if there are any specific restrictions on the Didcot to Oxford route using a Network Rail card that we're unaware of (I can't seem to find any) or if the customer sales assistant probably just didn't know what they were talking about and incorrectly rejected my wife's Network Rail card?