I am pretty sure this has to do with certain tax on the ticket.The AR tax applies only to nationals and residents of Argentina and I am assuming for the Argentinian equivalent of an SSN number.Also the ZK tax is a retention income tax:

PLEASE NOTE THE FOLLOWING NEEDED TO COMPLY WITH ARGENTINA
GOVERNMENT RESOLUTION 3450/AFIP;

1. THE TAX PAYER FISCAL NUMBER *(CUIT)/ (CUIT) OR (CDI)
MUST BE INCLUDED IN ALL INTERNATIONAL TICKETS ISSUED IN
ARGENTINA. THE CUIT MUST BE REPORTED IN THE RET FILES IN
THE PXDA FIELD.

2. THE AIRLINES CUIT NUMBER MUST BE INCLUDED AND MUST GO IN
THE RET FILES.

3. THE FOLLOWING TEXT MUST ALWAYS BE DISPLAYED IN THE
PASSENGER ITINERARY : ZK RG3450/AFIP.