Retiring a course properly
Hidden is not archived, and archived is not deleted.
Courses end. The version of a qualification is superseded, the cohort finishes, the trainer moves on. What happens next is usually that somebody hides the course from learners, which stops it appearing and changes nothing else. Hiding is a display setting. It does not stop enrolments, does not stop notifications in some configurations, and does not signal to anybody that the material inside is no longer current.
A proper retirement is a short sequence and it is worth writing down once. Stop new enrolments. Confirm all outstanding assessment is finalised. Take and verify a backup that includes the submissions. Move the course somewhere clearly marked as no longer current, so that a future administrator opening it knows immediately what they are looking at. Then, and only then, hide it.
The step people skip is the marking. A hidden course with a normal name is indistinguishable from a live one to anybody browsing the category list in three years, which is exactly how superseded material gets copied forward and used again. A convention as crude as a prefix on the name solves it, provided the convention is used consistently and written down somewhere other than in your head.
Deletion is a separate decision and usually a later one. There is rarely urgency, storage is cheap relative to the cost of being wrong, and the asymmetry is severe: keeping something unnecessarily costs a little, and deleting something necessary can cost a great deal.
There is a version of this that applies to whole categories rather than to single courses. A qualification is superseded, a suite of twelve courses becomes historical at once, and the retirement is done for the one everybody remembers while the other eleven remain in the live category looking current. A retirement checklist that operates at the level of the programme rather than the course catches this, and it is the difference between an archive that reflects the organisation and one that reflects whoever happened to be paying attention that week.