I think there is some trumping going on!
The TOC restriction is trumping the ability to use all but one of the stations in the Liverpool group because LM don't serve James Street,Central or Moorfields. I'd call that "trumping by stealth".
I suspected that this was the case. I'd say that this is a potential source for confusion amongst passengers and, as shown in the previous "Liverpool Stns" thread, railway staff.
Quoting Wikipedia on the reason BR introduced station groups-
http://en.wikipedia.org/wiki/Station_group_(railway)
"In the ticketing system of the British rail network, tickets are normally issued to and from individual stations. In some instances, when there is more than one station in a town or other localityespecially where these are on different routesit may be desirable for passengers to be able to travel to one station and back from another, or more generally to be able to choose which of the stations they wish to travel to. To accommodate this requirement, British Rail introduced a series of station groups: notional "common locations" to which tickets from stations outside that group would be issued."
Which was fine in the days of the joined-up railway without TOC-specific fares. But what we have now is a ticket that implies that it is valid from a group of stations by stating "Liverpool Stns" but then goes against this by specifying "LM only" meaning that in reality it can only be used at Lime Street.
For the sake of clarity and to prevent passengers from being done for not having a valid ticket on the Merseyrail loop, shouldn't these "LM only" tickets say "Liverpool Lime Street" rather than "Liverpool Stns"?
I know that it has been mentioned that this would complicate excess fares. Could someone explain how? Thanks.