Great result.
I wonder if it could be new referred members? I have not had any referred members yet, but what if the number at the top for this is only the recurring members from previous months and does not include new sign ups? Just an idea.
Otherwise unless you have a huge number of stories with small increases it does not even really show where the $15 increase is coming from, just a couple of dollars on the top story, and I would presume this trickles down. It would be interesting to see what the audience development page shows and if the update to that might just be out of sync with the earnings page.