I can tell by your scorn that you think it's ludicrous to assume that the TOCs would be using a modern computer database system for tracking railcards of all types. The thing is... most people would think that it isn't such a far-fetched notion. Database systems have become so commonplace that the thought of an organisation not using one for this kind of purpose is truly ludicrous. And given that a lot of railcards (especially YP ones) are bought via the internet, you really can't blame the passengers for thinking that there is some kind of centralised database.
As for your excuse of "some cards being bought on the day" - assuming that the database can be updated via an internet connection (most can), then this shouldn't be a problem at all, assuming that ticket office staff are on the ball.
Now, I'm not saying that there aren't some problems with this scenario - ticket checking staff not having access to reliable internet connections, for example, and there's still the issue of having to prove that you haven't just lent your physical railcard to a mate for the day, database or no. But these are not insurmountable problems. My point is that your apparent attitude - that such a database couldn't possibly exist or work - is misguided and defeatist.
And someone lent their Network card that day to someone else to use as happens ? It is in the T & C's , if you don't carry it you're liable to an excess fare upwards.