Join contacts with their licenses
Keep the files separate
Import contacts.csv as the people table. Import licenses.csv into a second table and relate the two on producer_id. Several licensing rows can point to one contact.
Count people correctly
Count distinct producer_id values after filtering licenses. A one-to-many join increases row counts even when the number of people is unchanged.
Read source and date together
Keep issuing_state, source_id and source_snapshot_date with each license. Address state describes the selected address on the contact row.