Hello Brian,
The items in the RSS structure are ordered by when they were posted, but the pubdate – which is what feed readers like Feedly or Mailchimp for RSS newsletters use – is the event date. So the Animals conference has the pubdate 12 Jul 2015 – that’s next year, so it’s always on top in Feedly or in MailChimp newsletters made from the RSS feed.
Does that explanation make sense?