Good point Manny. I'm not sure about single-radius slides. I had a Yamaha in the 1980s with a single radius; however, I think that the "ovatte" slide with a decreasing-radius type design is clearly a Monette innovation. Looking back at photos of old horns it seems clear that designers certainly had a wide range of slides with varying degrees of squareness and roundness, but I can't find any trumpets older than the 1980s with a round slide, so, maybe, Dave thunk that one up also.
Dave