It is pretty silly to research the laws of a planet but not the penalty for breaking the law. But the Edo also seemed to think the capital punishment for breaking any law was justified and reasonable so they may not have been very forth coming on punishment. Saying something simple like, "We have no crime, and when a law IS broken we're no different than anyone else when it comes to punishment."
Still sloppy for not getting specifics but the lack of crime and the fact that no one would likely do anything extreme enough to get punished probably didn't seem like it'd come up. Certainly any crime research wouldn't have gotten into "if you act like a dink and trample some flowers in the exact wrong place at the exact wrong time we'll kill you on the spot" and more into making sure that it wasn't a crime to do something that's normal or benign for humans/Starfleet but would be a illegal on the planet. (Like letting your dog pee on a tree or something.
Sloppy research, yes. But at face value the planet seemed harmless and peaceful so the idea of a death penalty for something trivial didn't enter-in as a thought to consider.