Past events don't show up in the "Past Events" sub-collection
The "Past Events" sub-collection inherits criteria from the "Upcoming Events" parent collection, so the combination of the two criteria (upcoming and past events) yields empty results. Check the bug #8827 for the complete history.
As a workaround, go to the "Past Events" sub-collection, click the Edit tab and uncheck the "Inherit Criteria" option. A permanent fix for this bug is expected to become part of a Plone 3.3 upcoming minor relase.
