If I get a non-new, non-unread thread at the bottom, as far as I can tell it’s always within the same category as the existing one. So I see this link (Offline for a few at some point - #3 by SpaceLobster) in this thread because they both are within Site Feedback.
No, this does not answer your question, but it is additional info. Maybe “New & Unread” is short for “… & Similar Topics”.