I'd thought Paul Renner, with his Futura experiments, was the first inventor of the detached lowercase 'r', but turns out the Speedball pen guys were years ahead of him.

Thanks to @goodspeed at @Typographics for suggesting Fonts In Use as a place to find true and varied references to specific moments in the past (in an age when AI gives a false impression of design eras based on a tossed salad of samey pastiches of that past).