Not so long ago I had to deal with the Austrian version of a Social Security Number and it turns out that using birthdates inside such a number isn't a good ide

Not so long ago I had to deal with the Austrian version of a Social Security Number and it turns out that using birthdates inside such a number isn't a good idea, since * Some people doesn't have a birthdate with which the Austrian state agrees * For those people the Austrian state at least assumes a birthyear with a birthday at January 1st or July 1st * This leads to overflowing the available numbers for those two dates * If a date overflows, they get SSN with month "13“. The 13th month can have as many days as needed (so > 31 is possible). * Now you have SSNs with a month part of e.g 2023-13-32. Why even bother with birthdates then?