The angle I take on this subject is quite a literal, use-of-English based one. The NRCoC state, taking a small snippet from the above [edit: on previous page] quotation:
The condition says ‘a train on which you are able to make’, not merely ‘a train on which you make’. A direct train between the origin and destination on the ticket is, indeed, a train on which you are able to make the entire journey without changing, even if one chooses not to make that entire journey. Being able to do something does not indicate compulsion to do it.
By my line of thinking, if someone wished to resume their journey, that would be fine too, but only if catching another train that runs direct from the ticket's origin to destination – because, again, it's a train on which the complete journey would have been possible without changing trains.
(a) You may travel between the stations shown on the ticket you hold in:
(i) a train on which you are able to make your entire journey without changing trains;
The condition says ‘a train on which you are able to make’, not merely ‘a train on which you make’. A direct train between the origin and destination on the ticket is, indeed, a train on which you are able to make the entire journey without changing, even if one chooses not to make that entire journey. Being able to do something does not indicate compulsion to do it.
By my line of thinking, if someone wished to resume their journey, that would be fine too, but only if catching another train that runs direct from the ticket's origin to destination – because, again, it's a train on which the complete journey would have been possible without changing trains.