Fascinating. While not conclusively proven, the Mitsumi catalogue pages from the late 90s/early 2000s suggest the following:
- Linear and tactile switches have separate series
- The first letter is K, the second letter is higher-level, and the third letter changes for linear/tactile
- The keyboard and assembly model numbers share the same series name as the switch technology
The yellow, tactile, Cherry MX mount switches are type KLT-11. The [wiki]Commodore Amiga 1000[/wiki] keyboard has assembly model KCT-A89YC, with full-size tactile switches, suggesting that those switches are KCT Type. Note that KLT and KCT differ only by the high-level letter, which is not unexpected.
Now we have KLM, which differs from KLT only by the low-level letter, which fits the general pattern, giving KLM Type for some subset of the switches.
As the Amiga switches (KCT) are Mitsumi mount, while KLT is Cherry MX mount and KLM is Mitsumi mount, it would seem reasonable to assume that the -11 code includes the keycap mount as part of its schema, although -11 is surprisingly simple as far as Mitsumi model schemas go. It's not safe to use only KLM/KLT type yet as there are unproven claims of clicky miniature switches — there's no video demonstrating this and no inspection of the parts, although you'd be brave to try as they don't come apart easily and are likely to break. There could be a third KL_ type for the clicky switches.
In fact, I had already documented something similar in rzwv's collection (another KLM keypad), but never recognised the significance of the model number on the PCB at the time.
Sadly, there's no trace on the Internet of KCT and KLM types and no mention of KLT outside of the keyboard community. All record of the existence of these switches seems to be lost.
