We would like to add this functionality into our site but we do not have access to the fare rules and tables beyond Dundalk and we don't know the routing rules (is Derry via Bleach Green or via the closed routing?)
The fares determination does not include cross border fares as these are a quasi commercial operation.
We have some of the data but have no way to validate it, Irish Rail removed most NI destinations from the ticket machines so we cannot walk up and run a list of combinations quickly.
The IE fares and NIR fares have no relationship at all
Irish Rail refuse to issue us with the internal fares guide and will claim commercial sensitivity if we go after it under FOI, even though the RUI fare calculator fare is basically the guide in online form, but we never ever had access to the guide.