@xssfox
My personal hell with postal codes was dealing with leading zeros here in the states. At one point in my life I was a volunteer for a folk music festival. In the days before internet, we maintained our communications throughout the year through the mail.

I was using a scripting interfaces to sql that interpreted leading zeros as an octal number. And, of course, as soon as you put it in excel, excel would just leave off the leading zero.

Looks like an integer, really a string.