One of the challenges while designing Automatic was the variety (and unpredictability) that exists in feeds. Although their structure is rigid, whether it’s RSS 1.0 or 2.0, or Atom, there is no “minimum set” of tags that must be included – meaning, there can be very little to no assumptions about the content. For Automatic, the decision was made to use the date tag to drive the matching and filtering engine. While it worked quite well, it eventually became apparent that it didn’t work when a feed “backdated” items (this usually occurs when a site allows users to create feeds “on-demand” by adding items, and an item that was added later might actually have an earlier date). It also didn’t work with feeds that have no date tag, which admittedly, are a small minority.
So, in order to support these 2 scenarios, the engine in 2.1 has been redesigned to be largely date-agnostic. The result is better support for feeds that backdate, and of course, support for feeds that have no dates.
For some subscriptions, depending on the rules set up and the previous matches, you may notice a one-time download of old items. These items were not previously downloaded by Automatic, but were ignored by the old engine. Going forward, the behavior should be the same.