Please don't add new answers. I don't understand how overlapping answers are supposed to be handled.
If the meetup does not take place or is postponed it will resolve to N/A.
Attendee is anyone who stays for at least 30 minutes during the meetup because they are (potentially) interested in the subject and not just because they happen to be in the same room doing something else.
The intervals are closed (include the endpoints) e.g. 6-8 is correct if and only if 6 people, 7 people or 8 people attend.