Country codes for locale

Is there a standard that the loc_CountryCodes that locale .country files should follow?

A preliminary stocktaking finds them to be all over the place. CH, B, S, N, and P look like the familiar vehicle licence plate codes (as do many other European .countries), but CAN, TUR, JPN, CZE, and USA seem to be randomly chosen from any number of (non-)standards.

A definitive list of existing .country country codes, plus what principles should be followed when creating a new .country would be useful, ideally included in the Autodocs.