Apple /// Datanetics keyboard

I learned with fascination some time ago that the Apple /// had both Datanetics DC-50 and Alps keyboards. Both took the peculiar route of having double-action arrow keys.I’m in contact with Meryl Miller from Datanetics, but he left the organisation before the Apple /// was created, and none of the Datanetics literature he preserved mentions double-action as existing. Curiously, the Datanetics double-action type has no “dash number” (DC-51-xx) which makes me wonder if it was created specifically for Apple and never advertised. It is given only as “SWITCH, DC51 DUAL ACTION (SARA)”, although the alternate action switch is given in the same way, and that was a catalogue option.All known Apple /// keyboards have had Alps-based keyboards, with one of two different designs of KFF series double-action switch. (The Apple /// keyboard is listed as KCC, not “KBB”, with KFF typewriter switches under the arrow keys.)Has anyone ever encountered one with a Datanetics keyboard? I am curious to see how they implemented double action. The switches are already double-pole capable, so possibly they made use of this with some way of staggering the actuation.