[FinnKuhn]

When I was a child I sent a postcard to my grandparents. I forgot to put the house number and addressed the letter to "Oma und Opa" (Grandma and Grandpa). Logically it should not have been delivered successfully.

Thankfully though, the postal worker knew my grandparents had grandchildren and therefore just asked the potential recipients for the name of their grandchildren to determine, which grandparents the postcard was addressed to. To me it's still a miracle that it got delivered at all.

[pseudohadamard]

Up until at least the 1970s you could do this with smaller places in Germany. My mother has some old letters with addresses like "$surname, $village near $larger-village, West Germany". I assume it was routed to $larger-village, they passed it on to $village, and everyone there knows everyone else so the postie dropped it off the next day.