Without particularly commenting on the correctness or otherwise of the original complaint,
I personally find the idea of station groups open to confusion unless a clear list of which stations
are in a group is publicly displayed.
Finding the
official station group listings seems difficult. An obvious search on Google "UK Rail Station Group" returns nothing official (only wikipedia)
https://en.wikipedia.org/wiki/Station_group_(railway)
It does contain references, but I can't see any of the references actually links to an official document containing the list.
The search "ATOC station Group" did return a suitable list, in PDF format.
http://www.atoc.org/clientfiles/files/group_stations.pdf
Is that the definitive list? Or the correct version? Who can say?
I couldn't find a list of station groups on the rail enquiries site. Surely it must be there, perhaps someone could offer the correct link.
If I went to a ticket office and asked for a list, would they be able to give me one?
Unless the list can be publicly displayed, I think using specific labels on the machine like "Liverpool Lime Street" would be better.
One entry for each station, then issue to "Liverpool Stations" with a note which stations this includes on the ticket.