As you mentioned in one of the earlier posts, if you go to Activity Completion, teachers, managers, etc can override the assignment completion check by clicking on it and confirming you intend to override the completion criteria. And...the way you appear to have it set up, the student can check the box as complete, even if they have not added anything. But you cannot override course completion--course completion triggers when all requirements are met (either by the student doing the requirements or the teacher marking the requirements complete manually).
The key for what you want is making sure both the conditions are met so the course completion can sync properly. If, as you indicate below, your sync is on, there should be no problem.
The key for what you want is making sure both the conditions are met so the course completion can sync properly. If, as you indicate below, your sync is on, there should be no problem.