You can stop scratching your heads about the other 41 prior confirmed detections. France and China did not sign the Partial (Limited) Test Ban Treaty (and have not done so to this day). So they had plenty of time to conduct atmospheric tests between 1963 and 1979. There are chronologies of all the atmospheric nuclear tests available, so count them if you want to.
The ionospheric shock wave from the explosion was detected by the Arecibo radio telescope in Puerto Rico short afterward, and radioactive fallout was detected in Australia several days later.
Senator John Glenn expressed serious doubt about the official version (cover-up) as did many others.
Whatever the truth of the matter is Israel has nuclear weapons it is confident will work. They were preparing to do a demonstration explosion in the Sinai to scare Egypt into ending an offensive there. It became unnecessary when Israeli troops succeeded in pushing back Egyptian force by conventional means.