The stuff about Gabelsberger shorthand sounds ludicrous to me. My father would write notes in a custom version of it until his death 2020.

Officially (i.e. in schools teaching stenography, back in the day) it was long ago replaced by "unified German shorthand" (Deutsche Einheitskurzschrift IIRC), but he always considered Gabelsberger to be superior.

Well, maybe he too was one of the 6 people in the world who could read it (or yes, maybe that was hyperbole, I'm not sure) :D