Now the real fun begins when the primary key almost never changes, and is considered never-changing by most businesses and computer systems, but there is an ext

Now the real fun begins when the primary key almost never changes, and is considered never-changing by most businesses and computer systems, but there is an extremely small number of cases when it does, in fact, change. Poland is like that for example. Our PESEL number encodes gender by whether one of the digits is odd or even. People with a legally-sanctioned gender change get a new PESEL, and a lot of systems aren't prepared for that. The Gender change process here is extremely long and arduous, and the number of transgender people was very low until recently, so most institutions weren't prepared to deal with it.