So if the debt is validated even though it was sold, it is owed?
Here’s where I expect crickets.
If the debt is validated, then it wasn't sold, by definition - it was legally transferred through some other administrative process. The definition of a creditor is one who hold a valid debt. The definition of a debt collector, in part, is that they are specifically not the creditor of the debt they are claiming to have the authority to collect, because the creditor is the one who sold them TITLE to the debt - not the actual debt itself.
In accounting, (which I suggest you study), debts are often settled by less than their marked value and then written off as partial losses for tax purposes. Once that is done, there is no more debt. If that settlement process consisted of the sale of the title of the debt to a third party, the original debt instruments are not transferred because by receiving payment the actual debt is settled, and thus there is no debt left to transfer.
Try to keep up.