Has nothing to do with it. The paper claim as to value can always be reinstated as to the amount the bad debt was sold for. But the surface value of the debt and interest and collection fees remain on the sale of the note to the collection firm. The only out for the debtor is to search for an improper filing.
I assume that you're suggesting the debtor look for some failure on the part of the lender to properly file and/or record the security instrument/mortgage/deed of trust, and (where required) to make whatever continuation filings or filings of assignments of interest as may be required by local law.
It can happen, and it's worth following up on, but don't hold out a lot of hope here, the title insurance company and the lawyers involved with the initial transaction and and subsequent assignment have a significant financial interest (malpractice!) in getting it right.