Howdy Elizabeth,
Good question!
If you chose to import the events that are already in your calendar then the plugin would create duplicates. In order to recognize an eventĀ as already existing on your site, and thus update its info rather than creating a new event, that event must have been created with the Facebook Importer. Your old events would have been created without the Importer though, and thus won’t be recognized.
However, when importing events from Facebook you can selectivaely choose which ones to import by unchecking them from the Import screen. So you could prevent them from being reimported.
Does that all make sense? Will that work for you? Please let me know.
Cheers!
– Brook