Please keep in mind that these were rules that you apply to a _toy_ project. You apply the rules once, blindly, even if they don't make sense to you at the moment. Then, when you work on a real thing, you may remember, for example, to create a dedicated PhoneNumber class with strict rules (e.g. E164) instead of a string that gets shuffled around with no one really knowing whats inside. Or you just forget the rules as a nonsense and move on.

You seem to be criticizing the 'rules' as if they are suggested for production code. You couldn't be seriously thinking someone suggest maximum-of-2-fields as some sort guideline for the real world.