In the main, one of the chief reasons for the huge increase in revenue staff by BR back in the mid 1980s, the introduction of many more RPIs to the old NSE business sector, was to combat widespread abuse of the old 'standard' return, which was valid for three months at the time.
It was always good for a smile when the outward half of an APTIS ticket that was 8 or 10 weeks old was presented for travel and you asked the holder 'Can I see your return half please sir?'
Being presented with a return half for the same journey, but with an entirely different ticket number and issue date lead to a bit more scrutiny and a few important questions, and almost always getting the same answer
'I didn't use that one, I got the ticket but didn't go because I got a phone call, or had to....(please enter excuse as appropriate)...'
The next question was always the same 'OK sir, then where is the return portion of this ticket please?' Inevitably the answer would be 'I've already used that one'
"Ah, so you came back, but didn't actually go then?"
Despite all the messing about with ticket validities and types in the intervening 30 years, it seems that in some areas, little has changed.