The United States (50 states and 1 district) is further broken down into the second part of its ISO 3166-2 code. For example- New Hampshire's 3166-2 code is US-NH. The second part (NH) is used.
These are alphabetized. When meeting directories cover multiple states, they are filed by the earliest alphabetical state. For example- Chattahoochee Flint Rivers Area containing meetings in Alabama, Florida and Georgia are filed under AL.