Then it sounds like you do retain access to concluded courses and the problem you are running into is pagination. By default, only the first 10 items of a list are returned in the Canvas API. You can either add a "per_page=#" query parameter (replacing # with a number higher than 10) or you could rewrite your code to look for the "next" link in the link header as described in the Canvas API docs. Alternatively, you could let the API do the filtering part for you by using the "enrollment_state=active" query parameter.