I would understand a similar journey to be the same journey as booked or one which is a subsection of the booked journey and costs the same or less. (Note that's completely unofficial.)
As for the supplement, it appears to be at IÉ's discretion/whim. Some friends from the Netherlands flew to Dublin and decided they'd be fine arriving into Dublin Airport at 14:40 and making Connolly for the 15:20 to Belfast. Needless to say that was a non-starter and they were charged €5 each at Connolly to revalidate their tickets for the 16:50. On the other hand, someone else who was supposed to be travelling with them (booked separately) and missed his flight showed up the next day and wasn't charged anything.
A charge might be justifiable if you booked an off-peak day return for €44 from Cork to Dublin and turned up wanting to get onto the 08:30 or some other service which would properly cost €61.
|