You create an initial attendance register for the year. This can form the basis for attendees for the rest of the year. Autofill adds expected attendees based on previous events.
Do not recapture each attendee for each event. Your staff can rather perform a roll call. They then tick contacts as being present or not. Add additional contacts as needed to these attendance registers.
Using this approach is much quicker for your capturers and makes it easier to manage. Most organizations have one person responsible for the calendar of events for the year. They create the events ahead of time, instead of letting capturers create events themselves. Upon creation each register has all prior attendees added but none of them are marked as attended. As roll calls are performed, this status changes. On a weekly basis or monthly basis management then review progress using the management report.