Worse, if someone else has to change the code, even if that someone is author a few months/years later, those concessions will be unknown, breaking the code in strange ways very hard to debug.

Don't forget that the code is now trivial: It's easy to see corner cases since the logic is so small and therefore quite "round". There is not really room for code "breaking in strange ways". It's rather that we can now think more mathematically and more uniformly about the program's behaviour.

It doesn't matter anymore if a given curiosity (like "-" options) is categorized as a concession or just as the way it's supposed to be. In any way it's the way that makes more sense from a mathematical standpoint. If there really was some client code depending on a curiosity, it's also easy to spot and change. But usually that's not even needed.