Entirely different fare matrix. The discounts are from the full adult price rather than the web fare. Discount on singles is higher than the discount on returns, and the discount on Dublin-Cork/Kerry/Limerick and Dublin-Dundalk lines (the reduction is only valid in ROI) is higher than the other lines.
The Railcard single fare is generally, but not always, slightly less than the highest online single, but is a walk-up fare.
Random example Heuston-Cork monthly return €78, railcard €51, 35% off (or 29% compared to a five day return).
Random example 2 Limerick-Cork five day return €37, railcard €24.20, 35% off
Extreme (low) example Heuston-Carlow monthly return €18, railcard €17.40, 3% off.
Extreme (high) example Connolly-Enniscorthy single (Fri/Sun) €28, railcard €13, 54% off.