The way our Part D coverage works is that each year we get a letter that we need to keep saying that we have I think it says creditable coverage, which means that the company drug coverage is as good or better then Medicare part D. Otherwise when we finally did sign up for part d we would have to pay a higher premium monthly forever. As long as you continue to keep drug coverage you are ok as I understand it, anyway.
No, it's not simple at all. No reason to feel overwhelmed by it, it's overwhelming :)