As you all can tell, some of the engine tag numbers posted above have more characters than others. It appears that the second and or first character(s) in some of the tag numbers has/have been omitted.
I believe the first character, if present, is the 'calibration' code. It should be different for 49-state, 50-state, California, Canada, export, etc. Perhaps a 'standard' (50-state?) calibration has no calibration code at the beginning of the engine tag number but a 'special' calibration does have a code? For example, K231A versus CK231A.
I believe the second character, if present, indicates a combination of ancillaries/accessories, i.e. Thermactor air pump or not, A/C compressor or not, power steering pump or not, etc. For example K231A versus 231A.
The three numbers and the succeeding letter should always be present. I believe the numbers represent the engine displacement & carburetor and the succeeding letter represents the calibration & revision level.