To add the missing customers back to the Event, and re-link the event to their sales tickets:
1. Bring up the Event in question and click on the Members tab.
2. Click on the first blank line in the Members list.
3. Click on the Add Existing Customer button, then select the customer from the list and click OK.
4. Select the Role for the customer.
5. Click the Save button.
6. Make sure the customer's name is highlighted in the Members list, then click on Go to Ticket.
7. At the top of the Sales Ticket, click on the Event lookup button.
8. Select the Event name from the list and click OK. When asked if you are sure, click Yes.
9. Click the Save, Done with Ticket button.
10. Repeat these steps for any remaining customers you wish to add.