What has any of that got to do with the original premise of the thread?A few examples, I'm intrigued as to how other people think these should be handled:
1) Passenger presents advance ticket for a long distance journey, involving a change of train, valid for the following day. Passenger insists he needs to travel now to visit a relative in hospital (be original please), but is unable to purchase another ticket. Warn him, but allow him to travel, on the basis that he should have to present his ticket again for the main leg of the journey. Passenger then leaves the train at a different station, not served by the operator or trains to the destination on the ticket.
2) Passenger approaches guard before boarding a very busy service in the middle of the PM peak. "I've got a ticket for the next train, but can I get on now?". Ticket is actually an advance for the train two hours later. Guard refuses. Passenger attempts to gain sympathy by claiming both that his boss bought his ticket and that he's finished work early and wants to get home. Guard still refuses. What if he had boarded without asking the guard and then been checked on the train?
3) Passenger presents guard with an advance ticket. Different TOC. Different time. Different day(!). Different route (same origin and destination). Told to buy new ticket. Refuses to pay that price. Tries to buy new ticket online - still an advance (and therefore still for the wrong time), still for the wrong TOC, still for the wrong route.
4) Another advance. Wrong TOC. Wrong time. Wrong route. "My friend bought it for me".
5) Railcard discounted ticket. No Railcard. "I am new here. My friend bought it for me".
6) Any number of the "pay when challenged" brigade, who regularly board busy services (in a penalty fares area) to travel one stop, knowing there's a very high chance that the guard won't get to them.
7) Advance ticket. Correct route. 4 hours early. "I just thought I'd catch an earlier train, I didn't want to wait".
What about these examples:
1) A passenger uses an off peak ticket at a valid time, but encounters Northern staff at Wakefield
2) A passenger uses an LNER train between Newcastle and Sunderland on a T&W Metro ticket
3) A passenger travels via Reading on a +via London ticket from Manchester to Basingstoke (or similar), and doesn't complete the double back via London
4) A passenger uses the Elizabeth Line on an All Line Rover
5) A passenger travels in accordance with the itinerary issued in conjunction with their ticket
(I could go on)
All real examples where tickets were valid and yet the train company concerned denied them their rights
And that's before we even get into customers actually mistakes, where the appropriate action would be to issue an excess or a new fare and instead passengers are issued penalty fares or prosecuted.