Thoughts on how to correct signer problem on multiple documents?

We sent out agreements to six clients - unfortunately, none of them added me as the secondary recipient. Once the client signed the document, the agreement is considered completed and I am unable to counter sign or add information. So, I asked my assistant to re-send them, apologized to my clients for the mistake, and my assistant pre-filled and sent them out. Except, she also forgot to add me as secondary recipient and we're back at square one. 

Is there a way to fix this without sending my clients a THIRD document to sign? I am not seeing any editing options. Only thing I can think of is convert to a JPG, reconvert to a PDF, and countersign in Mac Preview - but we lose having the documents in Acrobat for organizing purposes. 

Would love to hear options and thanks for reading.