In my "opinion", with a 6 week out of date Railcard which was used on both outward and return portions where the OP must have looked at his ticket wallet on numerous occasions when buying his ticket, putting it in his ticket wallet showing it many times etc., that to me proves that he is likely to of known it was out of date but still decided to use the Railcard thus proving intent, especially considering he used the TVMs at Bristol as opposed to one of the ticket windows.
Ah, now I understand why people are considering 6 weeks much worse than a few days. I keep my both my railcard and my ticket in my wallet, so I wouldn't have looked at my railcard when I bought the ticket (with hindsight it would have been a good idea to double check the date). I don't trust the plastic wallets that you get given because, in my experience, they are too easy to lose.
When I get it out for a ticket barrier or guard I look at it long enough to identify that it is my railcard, then I go back to doing whatever I was doing (struggling with luggage, reading my book etc).
From a guard's perspective there is normally one job for each customer - to check that their ticket is valid. When the task is so focused an error like a 6 week out of date railcard may seem unmissable (although the guard on the outbound leg missed it). But as a passenger who is more interested in their book than their ticket, it might be quite easy to miss.
Regarding the month being really obvious, the railcard expired in MAR, and I was travelling in MAY, so the difference between it and a valid railcard was one letter.
As for vending machines - they are faster than waiting in the queue at the ticket office. If they are being used to purchase invalid YP tickets then the vending machines need to be changed (or not sell discounted tickets), rather that automatically assuming the customer was trying to commit fraud.
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As far as I am aware, the only retail points for a railcard are the website and a staffed booking office. For the internet, even for renewals, you need either a passport or driving licence number, which I, and I suspect many other railcard users, do not have, therefore leaving stations as the only source.
You don't need them for renewals on internet-purchsed railcards. When I did mine all the asked for was my payment card details. I also expect the majority of railcard applicants would have a passport or driving licence, either for going abroad, driving (even if provisional) or getting into pubs. There will be a few without though.