iOS contains a setting that allows you to synchronize various intervals of past calendar events to your device. The setting intervals, as well as the steps for changing the interval, are provided below:
Events 2 Weeks Back
Events 1 Month Back
Events 3 Months Back
Events 6 Months Back
1. From the home page, tap Settings.
2. Tap Mail, Contacts, Calendars.
3. Under the CALENDARS section, tap the Sync option.
4. Choose the desired interval.