Analysis of information sources in references of the Wikipedia article "ISO 4217" in English language version.
The alphabetic code is based on another ISO standard, ISO 3166, which lists the codes for country names. The first two letters of the ISO 4217 three-letter code are the same as the code for the country name, and, where possible, the third letter corresponds to the first letter of the currency name.
Telex on the new 'Table 3' of historic denominations of currencies, as issued with my letter of 14 December 1988.