In American law only, and not in most people's usage anywhere. Probably more instruments were made and labelled as "autoharps" by other manufacturers in the decades before Schmidt registered the word than Schmidt themselves ever made. I'm certainly not about to stop calling my instrument an autoharp on Schmidt's say-so (it was made around 1900 and has a label saying "Müller's Autoharp").
I very much doubt if Schmidt's legalistic marketing chicanery had any force at all in South Africa in the 1940s. Tyson's band could call their instruments whatever they wanted, and we pretty much have to follow them if we want to make sense when talking about their music.
(And if Schmidt don't like it they can get stuffed. This proprietorial attitude to the English language really puts me off ever wanting to own one of their instruments - at least, not without scraping their logos off and putting a Hohner or Yamaha decal on it instead).