Hi there,
Thanks for reaching out. I’d be happy to help with your question.
When using that setting, it should preserve any changes that are made to your events after importing while still allowing other fields to be updated on subsequent imports. If you re-import an event after making any edits, Event Aggregator will omit any fields that have been modified with The Events Calendar, updating only the remaining fields that have changed at the source.
However, Aggregator will not delete events from your site that have been removed from the source.
As far as the titles go, I believe it uses a combination of title and date/time to determine which event is which. If the title has been changed at the source, it may be seen as a new event.
You can read more about the event update authority settings here: https://theeventscalendar.com/knowledgebase/event-aggregator-import-settings/
Hope that helps! Please let me know if you have any additional questions.
Thanks,
Sky