Now at some time, they (ITF Pioneers) moved to the natural movement & by the late 60s were calling it knee spring.

really? Wheres the evidence of this? Personally, I think its what they eventually termed sine wave.. hence why when the newer version came out, the pioneers reverted back to calling it "Natural Motion" Stuart

Geez, the evidence for this is all over the place. Interview of Kim Yong Soo, the Chief Instructor for the ITF in Korea in the late 60s. He was a Chung Do Kwan convert. Gen Choi saw him demonstrate in the 1960s & asked him to come over to his style. He did. Gen Choi taught him all 24 patterns. he graduated the 1st ITF IICs & then taught it. He said many, including himself, were resistant to the new way, as old habits were hard to break. Eventually, after keeping at it, he embraced it & said he saw the scientific basis for it. At the time, they were taught SW. he said the gen likened it to a car's suspension, which added speed, which was needed for power. He also used the term knee spring. It was all part of the package from the early days. It was the terminology, Korean to English that evolved over the years, as well as the emphasis.

Now knee spring was used in the 1972 text & everyone since then. It was the 1983 1st ed of the 15 volumes, that 1st saw the English use of the term SW.