What does the identification of Khālid ibn Makhlad as both al-Qaṭwānī and Kufan teach?

Titles and Affiliations, Etiquette, Transmission and Compilation — The Final Topics

• An affiliated narrator cannot transmit outside his town
• The two designations necessarily indicate two people
• An attached nisba makes further inquiry unnecessary
• The meaning of a nisba must be established through biographical research