It is pretty silly to research the laws of a planet but not the penalty for breaking the law.
"Law" is typically incomprehensible gobbledigook even to the trained policeman, and of no interest to the layman. "What is allowed and what is forbidden" is the relevant thing, and that is only a teeny weeny fraction of the broader concept of law. Surely Yar would have been studying the local rules of what can and cannot be done, and not wasting her time with meaningless studies of the law that is written around the subject in a language not intended to be comprehended.
A list of dos and don'ts would not necessarily include an attached list of sanctions. Tasha Yar never studied any "legal systems" - she studied relevant things which she defined as "customs and laws".