Hi decobiba,
it was Marcus Newhall, launching his book (and CD included) in November, 2008 who finally solved the longlasting mystery of this pattern as Stölzle Hermanova hut before 1958.
This pattern is not included in older Stölzle catalogues that are known so far (several between 1920 and 1950), which however does not exactly date the design itself.
I would therefore just say: post WWII
Hope this helps
:angel: