Alps PCB codes
Alps PCB codes are divided into four broad categories: “CH”, “12K”, “11K” and “AAA”. See Alps keyboard codes for more examples.
The meaning of 11, 12, 54, 56 and 57 is not known. In SMK part numbers, the leading code identifies the part classification, e.g. 401 for PCBs and 221 for relegendable covers. In which case, this number should not change. It could indicate the plant used, although that would put the PCBs for Japanese-made and Korean-made keyboards into the same plant. It is curious that the codes changed around the same time as second-generation SKCL/SKCM switches were introduced.
CH codes seem to be from the 1970s. Examples:
12K codes appear to span from 1980 to around 1988.
This has only been seen once, in what appears to a keyboard that Olivetti outsourced to Alps. The PCB code is 11KF013A. Helpfully there are no photos of the switches or the rest of the keyboard, so it remains a mystery exactly what this was.
These codes typically start 54AAA or 56AAA, but 57AAA has also been seen, and AAB might also exist. Unlike the preceding 12K codes, these appear to offer no details about the switches used in the keyboard.