Complex sentence: A rushed development program led to dozens of failures between 1965 and 1972 so that Proton remarkably did not complete its State Trials until 1977, at which point it was judged to have better than 90% reliability.
Split into simpler sentences: A rushed development program led to dozens of failures between 1965 and 1972. Proton did not complete its State Trials until 1977, at which point it was judged to have a higher than 90% reliability.