In APTIS days (they were the British Rail computerised booking office ticket machines) the words 'Any Reasonable' were added to tickets where there were multiple routes that the ticket was valid for. If a ticket had a specific route or route restriction (e.g. Not London), that would be shown instead. However, for simple journeys with only one 'route', (e.g. Wandsworth Common to Clapham Junction) no route was shown - there was no need for one. In technical terms the tickets was valid by 'any reasonable route' but there was only one, direct way to go.
The problem started at privatisation, when, to get the unpopular Railways Act through Parliament, the Government required that BR interavailable ticketing should be protected. Now, this was a good idea but the problem was the fares system was designed to sell BR fares, not fares from disaggregated companies. So a lot of bodging had to be done. One of these was to turn 'Any Reasonable' to 'Any Permitted' and create a routing guide.
All non-routed interavailable fares resided in the fares system as 'Any Permitted' flows, but APTIS continued to suppress them where there was only one route. However, when APTIS was replaced, the new systems all printed 'Any Reasonable' regardless of whether it was a simple flow or a complex one.
The whole issue of fare complexity kept being raised by stakeholders and at Ministerial level and one of the issue that kept coming up was the use of the baffling term 'Any Permitted'.
The underlying reason that the fares and ticketing system got into such a mess was down to creating a requirement to maintain through, national interavailable ticketing without ANY overall process to manage it - it was parcelled out amongst TOCs who were not allowed to discuss interavailable fares with each other and were given no guidance or direction on what to do apart from complying with fare regulation (which, until 2015, allowed considerable leeway for individual fares and in any case only covered a subset of fares).
But never mind, when the great and good get together, it is decreed that 'something must be done' even if it ignored the underlying issues, and one of the promises made was to stop using 'Any Permitted' on tickets that didn't need it.
Unfortunately, by this stage the TIS/supplier market had been left to code successive systems based on outcomes rather than processes, and when it was proposed that the 'APTIS' approach should be (re)adopted it turned out that quite a few systems were incapable of having no value in the route field. Hence the dot...
There are many understandable criticisms of the fares system but the people who tried to implement this were not 'inept' - they were trying to carry out orders based on sticking plaster solutions to 'improving' fares in an environment where no-one was actually able to direct or manage changes. Certainly with the new Railway bills laid before Parliament, the one really major outcome will be that a single organisation is going to end up back in overall charge of managing the fares structure (although Wales and Scotland will still dictate their own fares). It will be the first time since 1995 that an organisation is actually in charge rather than 'representing members'.