Vranjanka (Sano Duso)[South Serbia] dance history & background
Thanks to Dennis Boxell, John Kuo, and Edie Spear for sharing their knowledge and helping me piece this together.
Introduced to the music of Sano Duso by Dick Crum in the 50s, and to the music of Belo Lence by Dennis Boxell in the 60s, Vranjanka, Sano Duso, Belo Lence, and Deli Agus are all the same dance from South Serbia Vranje to Gnilane.
Sano Duso, the song most associated with this dance, is said to be derived from a 1930's opera "Kostana" which dramatized the life of a real-life Rom artistic figure. Songs from this opera became popularized and became accepted as part of the common repertoire of Vranje. Allegedly, Kostanka was at the premiere of the opera and had to dragged out screaming that the person depicted was not her!
In the 1948 Jadran film (now DVD) made available by Dennis Boxell, there is a segment of singers and dancers representing Vranje singing "Otvori belo Lence", another song also associated with the dance Vranjanka.