Exactly what tricky parts have I ignored? I don't think I've ignored the tricky parts at all. I've presented them in a working context that makes them seem less tricky in the first place.

Well, to start with - you left out teaspoons entirely. 48 teaspoons in a cup. 1/3 of a cup is also a very common measurement but no even number of tablespoons or ounces, but it's 16 teaspoons.