The course data is cached (to avoid having to make lots of database calls every time you load the main course page). The cache is cleared whenever something changes on a course (e.g. an activity is edited or a new activity is created). If you've created the data structures correctly, then doing something that will update the cache for the course (or purge all the caches via Site admin > Developer > Purge caches), should show the change.
If you're working with the code, then the function rebuild_course_cache($courseid) should be called.