WIPO ST.3
WIPO ST.3 is the World Intellectual Property Organization standard for the two-letter codes of countries and other organizations, such as regional intellectual-property organizations. It generally follows ISO 3166-1 except for the non-country entries. Current codes 

Rows in blue are not present in ISO 3166-2. Rows in yellow are different from ISO 3166-2. Codes AA, QM to QY, XA to XM, XO to XT, XW, XY, XZ and ZZ are available for individual or provisional use. References 

World Intellectual Property Organization
Country codes