If you want to be purely empirical about things, then of course, you will find there are no rules. You will always find counter-examples and changes in practice. However, if you are taking a purely empirical approach to interpreting classic men's dress, you are taking the wrong approach. You should be normative, in addition to empirical. Observe what has been done, try to understand why it was done, and then figure out what should be done. That's where rules come from.