What happens when a collections agency sells your account to another collections agency?

So NCO just sold my account/debt to Plaza Associates. NCO reported this debt to the three credit bureaus and i was working with them to take it off. So now that they sold it, will my credit report have two collections agencies for the same debt, or will NCO just fall off and be replaced by Plaza? Plaza seems to be easier to work with and may remove the derogatory item from my credit report, but i want to make sure that I don't pay the money before NCO is off too. Advice please.