Have you encountered the G4S clowns at Manchester ?
Or any passengers who are not either staff or forum members, i.e. most of them? Which is the point of this entire thread. I didn't break my journey, nor did I want to. I regarded what the guard did as wrong so challenged him with a theoretical question to which he had no good answer other than 'only obeying orders'.
How many passengers unfamiliar with the arcane rules of ticketing would have been aware that this change did not invalidate the ticket? It certainly looks as though it does. If an employee of the railway writes something on a ticket, most people will assume it is correct procedure. And this is the point, not that some pernickity nuisance forum member has spotted something dubious.
And as for the trite remark that 'anyone could have written that on the ticket', can I use that reasoning to reuse any ticket in future whose only grip mark is in biro, e.g. anything by Northern? "No Mr Northern Rail guard, it was me who circled that date, not one of your colleagues three weeks ago". No, of course I can't say that, so it can't be one rule for the TOCs/grips/RPIs and another rule for passengers.