Getting back to the Amati clarinets, I came across another maker in Austria, Musica Steyr, that could very plausibly have a connection to Amati, Kraslice. The key work is just too similar to have an entirely different origin, regardless of the country of manufacture. Compare the details of this Musica Steyr soprano with the Amati clarinets and known stencils. The only thing I see different in the key shapes is the C# key arm. The ring arms and other details are much the same. Late Amati clarinets also have a different C# key, more like this Musica Steyr example that is presumably Austrian in origin (photos borrowed for educational purposes):