Did you buy that car in 2013? Why Ireland changed its license plates.

Until Dec. 31, Irish license plate numbers included the last two digits of the year the car was purchased. 2013 has changed all that.

Is Ireland's new license-plate system really a result of superstition over the number 13? 

You wouldn't think triskaidekaphobia, or fear of the number 13, was much of an issue in the modern age, but you'd be wrong – at least if Irish news reports are to be believed.

As of this year, new vehicles in Ireland won't feature the "controversial" number on their license plates. Independent lawmaker Michael Healy-Rae tabled the idea in Ireland's parliament and, despite ridicule, it was passed in August and came into force on Jan. 1, 2013.

Until three days ago, Irish license plates read year of registration, county or city, and number of car registered. So the first car registered in Dublin in 2012 would be 12-D-1 and the 4,000th car registered in Cork would be 12-C-4000. There are currently 2 million private cars on Irish roads.

But the advent of 2013 sent a collective shiver through the owners of car dealerships. Or, more accurately, through those who represent them.

Mr. Healy-Rae, for example, worried that even a small drop in car sales brought about by superstition over the number 13 would damage the car-selling industry. So from this year onward, the year will be divided in two, so license plates on cars bought in the first half of this year will read 131 while those sold in the second half will read 132.

This isn't the first time license plate changes have been contemplated. In 2008, the Green Party, then a junior coalition partner in government, sought to remove the year from display altogether, arguing it encouraged consumerism. Nothing came of the plan, but today, worries are more likely to be that too few cars are sold, rather than too many.

Since Ireland fell into recession, car sales have fallen dramatically. According to industry figures, 2000 saw 224,000 new cars sold, while 2007, the first year of recession, saw 186,000. By the time 2011 rolled around, cars sold clocked just 90,000 — and 17,000 of those were bought as part of the government's "cash for clunkers" industry stimulation plan. Last year the numbers fell further, with just 80,000 new vehicles driving off lots, though this is arguably a slight improvement on the previous year when you take away the trade-in program.

And therein lies the real reason for the change.

Alan Nolan of the Society of the Irish Motor Industry explains that his group has been lobbying for change to the Irish license plate system for five years because it harms sales in the later months of the year.  

"80 percent of new car sales occur in the first six months [of the year]. The financial implications of that are huge in terms of financing, and there's a real danger of [car dealers] turning into seasonal employers," he says.

Just 317 new cars were sold in Ireland in December 2012, says Nolan.

Still, fear of cars numbered 13 isn't entirely irrational, he claims: "Some people do find having a number 13 on a car worrying. Some are genuinely superstitious, but you'd expect that to be a relatively small number these days. There is a more practical side to it, and that increases the anxiety: fear that other people are superstitious, making the car harder to sell in the second-hand market."

Conor Faughnan, policy director of the Automobile Association, Ireland's equivalent of the American Automobile Assocation, or AAA, says research performed by his organization bore this conclusion out.

"It is possible that the superstition was a small factor. Surprisingly to a convinced rationalist like myself, a small but significant number of people were wary of owning a 13-registered car, but it was primarily about artificially deflating the resale value," he says.

So, perhaps there is nothing to fear but fear itself after all. 

Car dealers, meanwhile, face 2013 with renewed hope.

"In some ways, the unlucky number 13 element turned out to be a lucky coincidence for us in the industry," says Mr. Nolan.