The mid-70s vintage Bridgestone/Kabuki "Submariner" bicycle also used stainless steel tubes, with aluminum lugs that were cast around the joints. And we (Trek) had Reynolds custom draw some stainless tube sets for prototypes in the early 1980s. N.B. these were not the modern 953 alloy Reynolds produces today. One of the prototypes got a spread in Bicycling magazine when it was displayed at the trade shows.

And Rene Herse's "Demountable" models were using couplers (but not stainless steel) way back in the 1940s.