Everyone invited to the event (the admin-uploaded roster).
Every login session by invited attendees -- a person who logs in twice counts twice.
Every company save across all attendees -- one attendee saving 3 companies counts 3.
Every intro request sent across all attendees -- one attendee requesting 3 intros counts 3.
Unique people invited (the roster).
Unique attendees who logged in at least once.
Unique attendees who saved at least one company.
Unique attendees who requested at least one intro.