Michael Black wrote:
Because it's a bug at google. When google took over the archive from
dejanews, you couldn't reply to old messages. Then one time when they
changed the interface, to be more useful for their own "groups", they
allowed replies to old posts. People like me complained, and that bug
was fixed. Then another iteration of the interface, and the bug was back.

You can reply to any Usenet post ever, if you can find it. You can
reply to a nonexistent one you invented. If your newsreader will not
let you do this, there are plenty of ways to create the headers,
including typing them in manually, and of sending the completed message
to your server.

George Cornelius