An "assignment" is the transfer of contractual rights to another. If a debt is said to be "sold", what they are selling is the right to collect the debt. Aka, assignment.
You know, after a handful of years of dealing with credit matters and a year of Business Law classes under my belt, I got a pretty good idea of what the difference between an assignment and sale, so thanks. Just an FYI, the "ownership" part is what matters. An assignment transfers rights, not ownership. A sale transfers both.
That said, I'll wait to see if this OP comes back and re-visits the thread.