Using a booked ticket on a later train.
 

Do I have it right that if you book a €10 web fare and you are unable to use that train that you can use a later train and pay the difference between the €10 web fare and the normal web fare?

https://www.irishrail.ie/home/terms_and_conditions.asp

You must pay the difference between the fare on that train and the train you where booked

So if it was 10 euro and the train you now want is 36 euro, pay 26 euro but only if that train has not been fully reserved.

No supplement applies to student and railcard tickets as no discount is offered

I have a very strong suspicion that if you attempt to do it though you'll be charged either the difference between your ticket price and a booking office single or just charged for a whole new ticket.

The difference in web fares was charged I'm told today in Heuston

My brother had bought return Heuston-Cork tickets, I had thought he had bought singles, so I was a little surprised when the surcharge was only €16. However this is correct, as it was €36-20=€16, not the €36-10=€26 I was expecting.

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Aboard the 1600 Heuston-Cork

Whoosh through Charleville at 1804
Arrive Mallow c. 1815
Depart Mallow 1825
Arrive Blackpool 1841 - "We are awaiting platform clearance"
Crossed the 1850 Cork-Tralee
Depart Blackpool 1857
Arrive Cork 1901

There was a Mark 4 set on platform 4 (saying Destination Heuston) and we arrived at platform 5. Passengers boarding the 1930 to Heuston (saying Destination Cork) were allowed use the tunnel to platform 5 at the same time we disembarked.

The train from Tralee would have been right behind us.

Are ye sure about this cos I've been explicitly told in the last few weeks, both by members of staff at the booking office in Tralee and at telesales that the price payable is the difference between the fare you've paid and a standard single ticket.

That text is still there, but I have to admit it is ambiguous. http://www.irishrail.ie/home/terms_and_conditions.asp

The understanding is you pay the difference between the fare your paid and the cheapest available at the time you actually travel.

Worst case is therefore the train you choose is sold out and the full fare applies, otherwise its the online price on the new train less the original fare which is consistent with what people have been paying

Even though web fares aren't available less than 60 minutes before departure??