I’m not sure I understand your question. My contention is that if a borrower pays back his loan to whoever he borrowed the money from, within the terms of the contract, then almost all problems are prevented.
you have to pay the CURRENT owner of the note.
Banks of sold promissory notes are just servicing agents. For eample Bank of America bought the rights to SERVICE mortages a short while back.
You have no provable chain of custody/title since the note was exectued, if the note even exists.
make no mistake, these are not accidents or a few isolated incidents.