Therefore are we to take it that for the purposes of complying with section 19(b) of the NRCoC that the call at a station where you change from one ticket to another must not have either a pick up only or set down only restriction?
... in my original answer - bound to cause controvesy.
For what it's worth, I believe that splits tickets probably ARE valid on services that "pick up only" or "set down only". But I'm sure that won't be the interpretation of gateline or on-train staff.
My 'interpretation', and that is all that it can be, is that the use of 'split tickets' for journeys on which one ticket expires and the next one is enganged at a station where the train stops for either 'pick-up only' or 'set down only', is
undefined.
If I am correct, then it would be unwise for anyone, passenger or staff, to assert that such an undefined combination is either valid or invalid.
However, if legal advice was sought on the validity of this specific combination of passenger, tickets, stations and trains, then having read all the publically available documents, it's my view that the balance of that advice would be to consider those tickets to be valid for travel.