Hi Michael:
I reached out to Sharon Horton with our BPC team and she offered the following guidance:
"If clauses (or folders) have already been exported/imported once, the clauses in the production system are protected from overlay in the import. So, if you export by folder, each new folder should export and import as expected. If you have new clauses that belong in the same folder as clauses that have already been exported, drag those clauses to a new folder, export that folder, import the folder then drag the clauses to the appropriate folder."
Regards,
Debbie Curtis-Magley
SAP Ariba Exchange Community Manager