They are normally listed in alphabetical order. The letters have the following meaning. This code consists of digits, letters, digits plus an optional suffix. A variant is used by the Russians. The first digits give the heater voltage rating, with the exception that the codes 7 and 14 are used to indicate 6.3V and 12.6V valves with a loctal base.
Letters specify the type of valve, but there appears to be no consistency of coding.
The suffix letters specify the type of envelope or base. The code is G large Glass envelope. Consists of digits, Letters, digits. Do not confuse with a US code. Mazda codes tend not to double up letters - L is used for multiple triodes also.