Why is a country's code sometimes called isoAlpha3, countryCode, or sometimes just code?

The attributes differ between procedures and restrictions depending on what entities are being described.

If you look at the "type" attribute, you will see we use "isoAlpha3" for the COUNTRY entities, "countryCode" within REGION entities (states, provinces, etc.), and "code" for NATIONALITY entities.

The plan is to bring these all in line with each other in version 3 of the product.