Shihap Kyorugi did not begin to develop in the late 1970's, it began in the 1940's and had a great acceleration in the 1960's, and progressed by leaps and bounds during each subsequent decade.
Right. Even back in the 1940s for example, sliding side kick (now known as Cut Kick) was being developed and used by GM UHM Woon Kyu at the Chung Do Kwan. He was nailing everyone with that, so much so that everyone copied him and the Side Kick became one of the Chung Do Kwan's signature techniques. Same thing with back kick and jumpin back kick, which was spin side kick and jump spin side kick back in the 1940s. GM Uhm was busy developing that as well. Today, one cannot be considered a complete competitor without a cut kick, back kick or jump back kick. It is in every competitor's bag of techniques.