OK, so the next departure time will automatically change to the arrival time of the previous ticket? If so, that makes it a lot easier but still doesn't guarantee you will be selecting the next available onward service to remain on the same train, so care does still need to be taken to ensure everything matches up.
When a change of train occurs, you also need to ensure you allow appropriate minimum connection times (do you have to look this up manually?)
You've just demonstrated how a request for (say) Scarborough to St Ives could be interpreted in a multitude of different ways, and the possibilities for changes, splits etc are huge. Do you have an easy way to look up all the possible itineraries and, for each itinerary, the possible splits automatically, or is it a manual process?
Of course, in reality, you'd rarely get such a request, because the vast majority of people making such journeys would surely prefer to book online.
But this thread is about whether it is better to buy from a ticket office; seeking advice is something else entirely.