Hi Scott
If I understand correctly, you are saying that people complete the Course once, and it ticks the completion tracking for activities. But the course is a refresher, and you would like them to re-enter the Course at a later date, and the ticks to not be there ?
Well, in fact this is an enrolment question. After a person complete the Course the first time, when they are unenrolled, you can have the behaviour set so all the completion data (in fact all data) is removed. This has the effect of making the Course seem like it's the first time the user has entered. Look under the Enrolment docs, specifically under the behaviour when unenrolling (If I recall correctly the default is for the results etc. to be visible again when a user re-enrols - which makes sense because if someone accidentally get unenrolled you would most likely want their progress to be restored).