If they physically didn't exist then a huge number of people would have to be in on it by the time scientists, engineers, contractors, funding agencies, builders, visiting school children and dignitaries. In teh case of SNO they also had to build somewhere to hide all the heavy water they borrowed. Proving the data isn't rigged I suppose is more difficult as only the scientists would have to be in on it. Though its worth noting that for 40 years the experiments didn't give the result we expected and in the late 1990's led to the discovery of neutrino oscillations. Presumably if the data was rigged then we would have rigged it to what we thought the answer would be. This agrees with the other main class of neutrino experiment which study neutrinos from nuclear reactors.