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Specifically, it was the "securities" or certain interest in such against the mortgage or a lien that have been sold, not the mortgage deeds ownership itself, i.e. the property buyer (mortgagor) still paid monthly payments to the original lender (mortgagee), unless in cases when the lender itself or its mortgage portfolio was acquired by another entity (e.g., Countrywide by BoA, IndyMac by OneWest).
In other words, the deed itself doesn't change lender / mortgagee name (for recording purposes) or physical place during the "securitazition" process, the bundle specifies the interest or claim on the deeds, not the change in "named ownership" or processing of the mortgage payments itself. If original lender which received the mortgage payments is still in business, it is responsible for taking possession of defaulted property.
Loss or gain in property value to the owner / interest-holder of "security" on that deed to whom it had been sold is an issue between a lender and the owner of "security"; it should have no relevance or be an issue in the foreclosure process in court.