As an ex-mailman, I can tell you that's not always true, especially in old villages, you miss a lot of numbers. And sometimes you come across residential areas where the numbers just run, so 1,2,3,. not to mention the a, b, c, d, e, f. maybe an idea to make another version?
@Bumblebea Is completely true! Indeed, that could still be a challenging version.! Add a residential area. And what do you mean by abcdef? Do you mean numbers 10 and 10 b, if a house has been built between them, for example?