Fully purging the knowledge base is a terrible idea, but having a "review timer" associated with each page might work. As pages approach, say, 1 year without ed

Fully purging the knowledge base is a terrible idea, but having a "review timer" associated with each page might work. As pages approach, say, 1 year without edits/actions, they get flagged for review. A reviewer can confirm if the info is still good, or needs to be updated, or needs to be archived etc. Assigning pages to owners is also important, so you know who's responsible for the content. In Confluence we just use Spaces as logical groupings but YMMV.