It’s entirely possible to create a railcard with a valid from date. I have bank cards with such a field.Very few people with the role of a guard can issue Penalty Fares. Sometimes ticket office or station staff can but even that isn't very common. Southeastern's onboard manager grade used to be able to issue Penalty Fares, and Southern's can but I don't know for certain if this is current. It's also quite pointless because these staff can't leave their train, and at least on Southeastern the train wouldn't be allowed to continue without them anyway. So in reality the person can just walk away and leave the train at the next station, something regulars would be well aware of. Revenue protection staff would leave the train with the customer if necessary to finish issuing the penalty fare. Finally, the old regulations said it was bad practice to allow the only member of staff on the train to be an authorised collector for PF purposes. So they didn't become authorised collectors and this has stuck. Chiltern used to have a number of these multi-skilled roles, but it seems there's been some opposition to the idea of safety critical onboard staff who are also revenue protection from the unions. In any case they also cut back on safety critical onboard staff a few years ago with the withdrawal of the 'bubble cars'. I'm not aware of any Northern conductors who are authorised collectors but don't exclude the possibility some are. If you're promoted into a conductor role you may be permitted to keep it, I don't know.
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Yes I also don't follow. Is it really sensible or reasonable to bar a customer who's 59 from purchasing an Advance with a Senior Railcard two months out, providing the customer qualifies for and purchases a Senior Railcard by the journey date? As far as I'm aware this has never previously been the case. Any attempt to invent this new restriction would be very anti customer.