I dont know about returning them, civ pro is civ pro, the main gist you want to learn is what the rules mean, and I don't think the casebooks are all that different, so probably no need to return. Often (if I remember right) the audios ID what casebook they are geared toward, but the biggest benefit is reinforcing the concepts irrespective of the cases, so I would not get too hung up on the casebook thing.