Americans back in the 50s used to do it almost the same, but flipped: for example, the old way to write the address (w/ zip code) for City Hall in Manhattan NYC
260 Broadway
New York 17
New York
but then the 17, originally a numbering system for big cities, became 100-07, the postcode 10007. (Compare the postcodes around London, EC1/N1/SW1/etc, which were originally just for sorting mail around the central city of England.)
Oh interesting. I had assumed that the transition to zip codes always added digits at the start (like San Francisco, which prepended 941 to the old codes) and didn't know there were places that inserted new digits in the middle instead.
