If you import a contact from the phone app and give Prim calendar permissions, the app will automatically import any events that you and the contact have both attended. For events to be imported the external calendar attendee’s email must match one of the emails listed in the contacts details. Currently, custom contacts can not import external events.
Prim tracks a last seen date for each of your relationships. Prim will import any events in external calendars where both you and the contact’s email were both attending. You can override the attendance field by editing the event from the Person’s view page. If the events do not exist on any imported calendar, you can manually add an event that you attended. The last seen date will be the most recent event date in the past with the attending field set.
The upcoming events page will show all future events you have manually saved in the application, plus any recurring events like birthdays or anniversaries that are imported from the phone contact app.