Buying a single code will have a total limits of 2500 attendees for all 3 events.

An event is deemed active when it is open for registrations. So in the case of a Summit, it is active whilst the summit is running.

Once the summit has finished, it moves from an active to a non-active status. The replays will remain open but registrations will be closed for obvious reasons. An Event in the non-active status does not count towards your active Event count.

in case of evergreen summits if registrations are open then it will add attendees to total no of empty seats available.
if limit is reached nearby to limit available, heysummit will send an reminder prior , informing about remaining attendee limits or upgrade plans if any.

we also have option to delete subscribers / email ids one on one right now inactive members , this empty attendee seats can be used for fresh registrations, bulk delete feature may release soon.

hope this may be right