Customer contacts duplicated across customers

My client has multiple customer accounts that belong to one legal entity (required structure due to other systems with which we interface data).  When setting up the contacts for the customer accounts, users have been typing in the contact name (not selecting from the LOV once the initial contact is created).  As a result, there are duplicated person parties now.  This would not be an issue, except we are now implementing iReceivables.  As we set up the external users, it becomes obvious that the contacts (person parties) are duplicated.  I have been using the party merge on the person parties