It is not enough to know the rules. It is also important to know the exceptions and where the rules originated.
And then, along with those areas, it can help to know the proclivities of those who enforce the rules and which modifications, however unintended, they may insert in that enforcement. Such changes made be the equivalent of amendments.
What is a good demonstration of knowledge? Being able to provide a brief, accurate, and understandable explanation to someone who has no background in the subject and who is eager to be elsewhere.