I have 2 contact lists, on with clients most up-to-date data and another with the client's month-over-month data. When updating an existing month, I first authenticate the client most up-to-date contact list, then once successful I authenticate the month-over-month to select the month I would like to update. The month-over-month updates as it should, however in the most up-to-date contact list a contact is added, creating a duplicate contact.