Our social security number is made of YYMMDD-xxxx. So there is only 10000 different people who can be born on the same day in our system.

Along with that the numbers that ends on an even number belongs to females and the odd numbers belongs to men.

So only 5000 women and 5000 men can be born on the same day.

Let's say that it's a popular day to be born. Like 9months after a holiday. And then you add a lot of immigrants throughout the years. Not just these last few years but all the years. We've had a surge of immigrants for 50-60 years.

And there is our problem because they didn't think we would get so many immigrants to fill the qouta.

So what they have done is that if the days around their birthday is low then they will get another day than their birthday as SS. But let's say that the whole month is taken then they will switch to 18YYMMDD-xxxx instead. Which will fuck up some systems.

Some years ago this wasn't a problem and most places like the dentist and such would only ask for YYMMDD-xxxx but since the quota got full they switched to YYYYMMDD-xxxx.