A few people have mentioned to me that the Email Alert for this blog on occasion resends old posts.
I've been looking into this the past few weeks, but not solution has been suggested to me from various help forums besides resyncing the feed that generates this email; which I've done, but the problem is still occurring.
It's not an isolated problem. I've found other people asking about it online as well, but no one seems to have an explanation or a fix. It has to do with the Feedburner RSS feed.
So unfortunately, we are stuck with it for now. If you are relying on the email alert, make sure you check the dates of any events before you charge off to the venue, in case it happened months ago.
Note that this is only a problem with the email notifier, the blog itself is still working fine.