I think that advice makes sense in the context of cryptography, where the consequences for getting it wrong can be quite serious indeed. I don't think it holds true for something as unimportant as a date parsing library.
2) Many people (especially the elderly) take enough medications on different schedules that managing them all would be a significant cognitive load for anyone
It’s just an illustrative example, though. My point is getting dates right (including parsing their string representations) often matters quite a bit. If you disagree, let’s argue about that rather than quibble about the minutiae of the example