TVMs do not usually sell all tickets valid from that station to the final destination. Most will not sell monthly (+) seasons, or rangers/ rovers valid from that station to the final destination.
In general terms, it seems absurd, perverse and unjust that the holder of an A to B season ticket who wishes to travel from A to C, on the last train of the day, would be effectively forced to buy an new A to C ticket rather than a valid B to C single simply because:
1) the TVM at A will not sell the B to C single, and;
2) he/she cannot risk not finding the guard, or the guard being unable to sell the B to C ticket, before the train arrives at, or passes through, B.
If a train passes through the point to which a ticket was notionally valid, without stopping at any intermediate stations beforehand, would the RCCA offence still apply, given that there is no opportunity to leave the train at that point?