If they sold it to the CA, then the OC should report a $0 balance. If they simply hired the CA to collect on their behalf, but retained ownership of the debt, then they will continue to show a balance.
If the OC sold it, they have to report a $0 balance on any CRA they are reporting to, regardless of which CRAs the CA reports to.
If they are still reporting a balance, they probably didn't sell. If they are reporting a $0 balance, they probably sold it. But you can call them and ask if you want to know for sure. You can call the CA and ask, too.
Not sure of the legal avenues you have to demand this info if neither the OC or CA answers your question.