I appear to have beaten you to it, Henry; I have moved it to RO.
We do not have a policy for deleting posts. Once a post has been published on a website like this, it can be indexed in archiving search engines. Also if you delete a post, it makes nonsense of the subsequent replies. We moderators occasionally remove material because it has something wrong with it, or it has mistakenly been posted twice, but apart from that, posts live "for ever."
People occasionally find 5-year old posts helpful, so old discussions are retained as a resource.
We have even restricted the ability of users to edit posts after a certain period, because people were deleting the 1st post of a thread and the remainder made no sense.