Personally i think the Complete Lesson button is not a bad Idea. It will always be hard to integrate courses which were already available earlier in the rating. People who already did study the course could use this second walkthrough as a possibility to improve and strengthen the skills first learned, but i think many do not really want that, if they are forced. And if we are all honest, badges are nice but it does mean nothing in the end to really improve your artwork if the work is not really done. Even if there is no such autocomplete function people who want to cheat will surely get some possibilities. And in the end a rating is not really easy, i mean someone could spend a lifetime really learning for example the figure drawing course and putting his heart into it, while another does 40 courses by only skimming over it. A comparison between those two kinds is surely not easy. Maybe a function like the one Udemy provides, where you can hide courses which you did finish, or you which to ignore until a later date in a second List would help to keep people on track, and the course list short and orderly. The "Course finished" button could be only to mark the courses for people as finished without giving them any points to keep track.