unquestionably invalid on the return
It seems that elements of what might reasonably be regarded as the "contract" contradict each other.do
There is a legitimate use of the crazy-looking "journey":
I can recall many instances where my travel followed that pattern. (e.g from Northampton to Birmingham to meet a friend for lunch, then from Birmingham to Stechford to visit my granny)
If the average passenger wanted to do that, and both NRE and the train company selling the ticket said they could, it may not be unreasonable for them to assume that is the contract.
It would seem unreasonable to expect them to look up the Conditions of Travel just in case it said the opposite.
it's a contractual matter of the company fulfilling its contractual obligation to convey the customer to their final ticketed destination.
But the passenger might be said to have bought the ticket on the basis of more than that.
The advertised basis - the "journey" described before purchase - is that you can go from A to C, then B.
The fact that the "allowed" train service from A to C stops at B - and even the apparent fact that if the "journey" is valid the passenger can break it - are in the context of that advertised "journey".
If the passenger wants to go to C and has bought the ticket on that basis, and if the ticket is valid, it would be sensible to allow them to travel on an earlier train calling at B rather than force them to wait for a later train that doesn't.
On the other hand, it seems hard to support the idea that the validity is "unquestionable" or the idea that RPIs would have no grounds for asking for details. The ticket is supposed to be subject to this:
National Rail Conditions of Travel said:
13.4. If you travel beyond the destination shown on the Ticket, you will be treated as having joined the train without a valid Ticket for the additional part of your journey.
The question* seems to me to come down to which should take priority: the contractual "obligation" to alight or the contractual "right" to travel further.
* leaving aside questions about whether TOCs are bound in principle to honour what retailers sell.
How to decide that? It might be held that the advertised "journey" as NRE calls it, is more prominently stated to the passenger than Condition of Travel 13.4 forbidding travel from B to C.
They are perhaps more likely to see the itinerary than the condition.
That interpretation - that the condition can be overridden - might be helped by arguing that although 13.4 looks strict it isn't: you may in some circumstances legitimately "travel beyond the destination" on a non-stop train to double back.
Consumer law says if a term can have more than one meaning, the interpretation more favourable to the customer prevails. A passenger might argue that the term of the agreement purporting to allow travel via C to B can mean "and this overrides 13.4", that it as a matter of principle overrides any other condition, or that it does in practice because it is more prominent.
The Ramsgate case is different in that here a retailer is offering something for £6.40 which NRE advertises for £75.60.
It would seem unlikely someone would be penalised for being ripped off like that. Perhaps it might be argued that if that is a valid "journey" because NRE appears to go "out of its way" to offer it, the Stechford one is too. Or that that doesn't apply, because the Ramsgate one is priced so differently.
Perhaps someone might argue about the meaning and relevance of condition 16.3 and/or the info box below it.
Someone might argue that if the passenger isn't intending to go to C and B in that order, that indicates a likelihood that they are evading the right fare, perhaps in conjunction with other specific circumstances.
Perhaps there might be other arguments.
But the arguments need to be on the basis of what can be reasonably be taken - as a whole - as the contract or elements of it.
Maybe sometimes questions about ticket validity in practice come down to the specific use of tickets by specific people. A person with knowledge of the Conditions might be viewed differently from someone without.
I confess that this response is because some of the issues interest me in the abstract rather than because I think this type of case is of any great importance.