Not sure but I do have some old spam topics that are now ~disabled~ as it were - there is no lock icon on them but you can't post to them anymore. Taking that into account that is most likely what is going on. They just kind of disable after so long since it is spam. Other areas don't seem to have this set up. Like I have Rps that are archived so I can reference them and they haven't posted in for over 2 years. I could still add a reply to them if I wanted.