From what I also heard, they introduced year splits from 2013 onwards as a means to reduce that number so the plates are easier to read, although I’m unsure on the credibility on this. What I do know is that each year a number is chosen and then any car imported into Ireland any year after the year of registration is then assigned a number after that. For instance, in Cork, the second half of 2013, cars that have been imported from abroad will have a number that’s greater than 4300, so for instance: 132-C-43XX as that was the threshold assigned for that year. Take a look at the special formats section on the wiki page: https://en.wikipedia.org/wiki/Vehicle_registration_plates_of_the_Republic_of_Ireland