The first Robeson knives were imported by Millard Robeson from England and Germany exclusively. This continued from 1979 until 1896 when Robeson began manufacturing knives in the United States. Since inception, the company has gone through several reorganizations & eventually ended up as a Queen Cutlery brand.
I think the sunk joint involves a different tang shape/size and perhaps placement of pivot pin as well. I don't think buffing down the corners of tang is how a sunk joint is achieved. It would interfere with the blade/spring meeting when fully open. kj