I had wondered what the contractual position would be as the ticket was free? I guess though its not different to the situation if you'd paid for the ticket? For the concessionary card, Welsh Government have paid instead of the passenger.
Note that the travel card itself is not a ticket, you are required to use it to get a ticket. If you have had no chance to get an actual ticket for your journey, your contractual position might be weak.
Unfortunately there doesn't seem to be any way to obtain a ticket on-line or from a TVM, only from a TFW booking office (where there is one, and it is open) or from a TFW guard on the train. Non-TFW booking offices and guards don't seem able to issue them (or at least, none that I have tried, such as BHM or EUS).
Some delay repay websites (such as Avanti's) refuse to accept a zero value ticket! Okay, you aren't going to get much compo for a zero value ticket, but you may want to use it for the last part of a split-ticket journey.