Hi James,
How about if you were to do this instead:
- Push the form submitters into a shared list from the vack
- Create an attended contact field for the event.
- Export the shared list using a view that includes all you need including your new attended field
- After the event you could re-upload and get the information straight into the contact field.
After the event you could push people into shared lists for attendees / non-attendees / walk-ins based on the value of the field, and then remove the contact field so as to be able to start afresh each time without reaching the 250 field limit on the contact record. You wouold have a record held in the shared lists, so don't need the field any more.
Hope that is helpful.
Phil