What is the ruling when witness testimonies regarding the scope of power of attorney differ by addition?

Primary text

If one witness testifies the principal authorized him to sell his slave, and the other testifies the principal authorized him to sell his slave and his female slave (jariyah), the agency concerning the slave is ruled valid based on the agreement. The addition by the second witness concerning the female slave does not invalidate the authorization concerning the slave, thus it does not harm the established agency regarding the first item.