This can get ugly in a hurry. The CCs sound like they are linked to document properties that are being wiped by Sharepoint. It is possible that this is happening because you may have upgraded your Sharepoint version or the document properties have been changed in some way which causes Sharepoint to overwrite them instead of importing them.

I would compare the xml files embedded in the docx files before and after they get wiped to see if you can spot a critical difference. You may be able to adjust that namespace or schema to match the xml that Sharepoint inflicts on the file coming in. Do you know how to get at the custom xml files in Word?

Did your client load the files into their Sharepoint site before sending the files back?

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Andrew Lockton
Chrysalis Design, Melbourne Australia