Very little is known about Jelco switches. Hopefully with time, more will be discovered.
The only semi-confirmed type is JKS-91. The part number was provided by Australian manufacturer Microbee Technology who used them in their 80s home computers. No official literature of any form has been forthcoming, not even an invoice with part numbers on.
A switch was found in the “TOuSJE” keyboard, with characteristics very similar to JKS-91. In particular, it has a vertical contact module with a horizontally-protruding rubber dome. This keyboard, PCB model JMC-100B, was made by Datacomp, a useless company who utterly refuse to respond to questions, including about their own switches. Most switches in this series were SMK J-M0404 series, with no apparent reason for a few being of another brand.
A very similar keyboard, PCB model JMC-82 and Datacomp model DFK-505, was found with solely these switches; this keyboard was sold by Phoinix. Here, you can see that the contact system is something like Futaba MD series.
These switches are not identified at all, and are not branded, but they seem to also be Jelco.
Note that both keyboards have the same number of keys, so the JMC codes do not indicate key count.
|Jelco Co., Ltd.||US 4631378A||Push button switch||1984-10-19||1986-12-23|
|Jelco Co., Ltd.||US 4831223A||Push-button switch||1987-03-25||1989-05-16|