Whilst there is nothing 'in the public domain' AFAIK, there is in the iKB (formerly 'The Manual'). The origin and destination "should" be the same and the ticket type "should normally" be the same. This is the same for Family and Friends, Disabled and Two Together Railcards.
However, some staff seem to know as much about iKB as they do the Routeing Guide and others don't seem to care, so YMMV.