title: Rails gem - Public Activity for earlier posts
body: <p>The gem does not recognize earlier post which were created before the gem was added.
  It only started working, when fresh posts were created. Why was that?</p>
  
  <p>And, how to have those earlier posts get covered by <code>public_activity</code></p>
  
  <p>Thanks.<br>
  <em>Gem setup according to author site.</em></p>