The National Lottery has apologised after four top prizes totalling €180,000 were not included for players to win in three of its 178 scratch card games since 2014, when operator PLI took over the licence.
In a statement, the Lottery said the omission was caused by human error.
The prizes were not available in the two versions of the Congratulations game and the Diamond Bingo Doubler game.
The mistake was discovered following an internal review of all National Lottery products over the last six weeks.
The Lotto, EuroMillions, Daily Millions, digital games and other National Lottery products were unaffected.
A New Year's Special Draw will take place on 6 January for 180 "will be won" prizes of €1,000.
Anyone who enters the Christmas Bonus Draws will be automatically entered – the bonus draws for players of Hampers Sweets and Treats, Merry Money or Christmas Countdown scratch cards, which were bought after 1 October.
The Lottery said it will fund the cost of the special draw and will donate any additional funds to Jigsaw, the National Centre for Youth Mental Health.
National Lottery CEO Andrew Algeo said: "We are deeply sorry for these errors which should have been fixed before the games went on sale."
He said new controls are in place to ensure it does not happen again.
Meanwhile, the Office of the Regulator of the National Lottery has said that it became aware of the errors last month.
In a statement, it said that once the anomalies were known, its priority was to find and implement a solution to return the value of the prizes to the players.
The statement added that officials are now "examining what breaches of the Act or Licence may have occurred and have written to the Operator to commence the formal process prescribed in the Licence in this regard".
National Lottery spokesperson Paul Bradley said other games are "completely unaffected" by the error.
Speaking on RTÉ's News at One, he said the Lottery has changed their "processes and controls" to prevent the situation from happening again.
"We are desperately sorry. We want to ensure that people are treated fairly. It's very important to us that our players are reassured.
"You must remember that the total amount of prizes that are impacted are less than 1% of 1% of all our prizes in the last five years".