It also allows for Ascension Island (properly part of Saint Helena). Eric Muller has created a website that keeps track of changes in the GEC codes for primary subdivisions.
ITU - A number of Web pages say that the ITU country codes are being used, mostly to identify radio transmitter locations. These should not be confused with several other ITU codes, mostly numeric, which are used as dialing prefixes (e.g., ITU-T Recommendation E.164 ). The GEC country list differs from ISO 3166 in many minor and sometimes surprising ways.
It maintains an authoritative list of ISO Alpha-2 Codes . See the changes in ISO 3166-1 page for the change history.
Its list is coordinated with a list of countries used by the United Nations Statistics Division for reporting purposes. I have also written a page about using ISO 3166-1 in software.
Instead of Tanzania, there are Tanganyika (EAT) and Zanzibar (EAZ), dating back to before 1964 when the two countries united.