The Event entity contains a business rule for partial recurrence records.
Data Archive will archive a recurring Salesforce event only when the full transaction (the entire recurring event) is selected with reference to the given filter criteria. You must give the values so that the entire recurring transaction will be selected. This business rule updates the interim table PURGEABLE_FLAG column to 'N' if any partial recurrence records are found in it. For more information on partial recurrence events, see the topic "Partial Recurrence Activities" in this chapter.