Each former country name in ISO 3166-3 is assigned a four-letter alphabetic code.
After the expiration of the transitional period, these codes are free to be reassigned.
Currently, a few ccTLDs using deleted alpha-2 codes are still active or being phased out.
However, alpha-2 codes which were deleted before the popularization of the Domain Name System in the late 1980s and early 1990s were never used for the Internet's country code top-level domains (ccTLDs).
ISO used to announce changes in newsletters which updated the currently valid standard, and releasing new editions which comprise a consolidation of newsletter changes.