Hi,
The part number is the following:
ASA-CSCX-YP-ZY
where X is your CSC model, Y is the number of seats of the license and Z is the number of years.
For instance, if you need a 2 year plus license for a CSC10 with 250 seats, the part number would be ASA-CSC10-250P-2Y
Regards,
Nicolas