In certain scenarios, Google Appointment attachments will also exist in the source account's Drive. This is most common when an appointment attachment has been uploaded to an event and Google uploads a copy of the file to the user's Drive so it can insert a link to this item back into the calendar appointment.
If migrating Google Appointment attachments using the Google Destination Platform advanced setting 'Migrate Attachments' and enabling both calendar and drive items for migration, this could result in broken calendar attachment links. To avoid this, we will migrate a copy of the file as part of the calendar migration and link this ID to the calendar event. Then, during the drive migration, if the same item existed in the source Drive, we will migrate again as a separate Drive item, resulting in a duplicate file. This ensures that we are able to keep the attachment link on the migrated calendar event correct.