What is the unique key when re-importing adjusted CSV file?: email adres?
Include header rows, nice, but if the CSV contains other non valid header rows can those just be ignored instead of import fails? Also, using CSV import, only fields what are available will be overwritten with email as unique key?
E-mail is the unique key. All fields that are linked to that person (because of the persons Person Type) will be updated.
We are specifically failing incorrect headers rows, because this allows you to correct errors before doing the entire import.