If you see an Online Course in the Learner User Interface (UI) that has an Expiration (or other) Date that wasn't set up through the course's Availability settings, it's likely that the date was inherited from a Curriculum. Online Courses that are also contained within Curricula can inherit Due Dates, Expiration Dates, and Access Dates from the Curriculum that they are part of.
For example, if you have a Curriculum that has an Expiration Date of September 1, 2017, this Expiration Date will be inherited by all of the Online Courses within it. Curricula will also overwrite any existing Due Dates, Expiration Dates, or Access Dates for an online course when included in a Curriculum which the Learner is enrolled in.
If you require multiple Online Courses that have different Due Dates, Access Dates, or Expiration Dates, it's recommended that a Course Bundle be utilized instead of a Curriculum.