The only thing that has to be "logged" is that you did such and such unit/lesson in accordance with the regulations for pilot logbooks. Unless it's part 61, the course should provide the necessary reference for the maneuvers/tasks and these wouldn't have to be individually written. That said, there's no regulation prohibiting someone from entering more. Most examiners and schools understand that "less is more" approach is best, since it leaves the least amount of liability for all involved, but some like to write a "checkride passed!" or "good job" in the logbook. I wouldn't want someone writing "unsat" in my logbook either.

You are totally right, but a savvy person could look at the logbook, look at the lesson number, see that in the course you got to lesson 29, the highest number, then did a previous lesson, then did lesson 29 again. That doesn't take a rocket scientist to figure out. Heck, I'd rather see this, since it tells me the school was doing things right and not just passing people arbitrarily, maybe an indicator of quality rather than being just a pilot-mill.