Well, at least we know Heyworth sold clarinets with the Lucian Bassi name on them. And it could indeed be the same Czech clarinets like this one Lucian Bassi we have before us. However if Lucian Bassi is a stencil name, it is plausible that other makers could supply these at different times. Certainly Bohemian mystery maker #2 put names other than Lucian Bassi on the same product, for instance Pierre Dumont or Grenadier, or no name at all.
The clarinet illustrated in the ad is probably one of Heyworth's other offerings because the humps in the throat trills are rounded, not pointed. The Bassi clarinet is not illustrated. I do think that 1936 would be a realistic time for the examples I see from Bohemian mystery maker #2. These have solid nickel-silver keys, many other details point to pre WW2 production.
From the history given here:
http://www.amati.cz/en/company/historyAfter the WWI, production quickly recovered. Between the two World Wars, there were 59 musical instrument manufacturers. Among the biggest of these firms were: Bohland&Fuchs, Hüller&Co., A.K.Hüttl, Julius Keilwerth, Karl Püchner, Adolf Rölz, Ant.Kohlert etc. However, during WWII, many plants ceased to exist, while others served military purposes.
In September 1945, a Cooperative of musical instrument manufacturers was established in Kraslice. And because the production of both wind and stringed instruments was anticipated, the Cooperative was given the name "AMATI".
If Lucian Bassi is from 1936 and is the same as the Pierre Dumont (not the French stencil with the same name), the same as one marked Grenadier (not the Pruefer Silver Throat stencil of the same name), and the same as two Czech siblings I picked up 2 years ago, then there are 59 plausible makers and Amati, formed in 1945, is simply not one of them. Bohemian mystery maker #2 was absorbed into Amati, and later Amati clarinets therefore have some characteristics shared with many of the other makers absorbed into Amati.
I'll get you a few photos of a Bohemian mystery maker #2 next to a much later Amati. I think it could be said that Amati keywork in style could be a derivative of the style of Bohemian mystery maker #2. It is not the same metal and there are quite a few differences throughout, the G# notwithstanding.