Contact Addresses: Country does not exist

If the issue concerns you enough I would reach out to Apple directly and provide your feedback. It's likely an oversight in the development. In the meantime you can just manually enter the Country name in the field.

Apple typically uses the ISO 3166 standard for country and region codes in its software and services. And ISO 3166 does include specific codes for Guernsey and Jersey:

• Guernsey: The ISO 3166-1 alpha-2 code is GG.
• Jersey: The ISO 3166-1 alpha-2 code is JE.

However, the implementation and presentation of these codes in user interfaces, like address books or contact lists, may vary. Apple might choose to display a subset of these codes based on several reasons:

Guernsey and Jersey, as part of the Channel Islands, have a unique political status. They are British Crown Dependencies but not part of the United Kingdom or the European Union. This unique status can lead to confusion or oversimplification in categorization.

Developers often prioritize countries and regions based on market size and user base. Smaller regions, especially those with unique statuses, might be overlooked.

Including every territory and region in the world can make user interfaces cumbersome. Developers might opt to simplify lists for usability, inadvertently omitting some regions.

Country and region lists in software applications may not be updated frequently, leading to outdated information that doesn't reflect recent geopolitical changes.