It only snookered those who wanted to be snookered. No other intelligence agency in the world concluded that Iran had cease its nuclear weapons program. The so-called National Intelligence Assessment was a politcal document intended to constrain President Bush from attacking Iranian nuclear facilities prior to leaving office. It was hardly even a fig leaf for those who prefer bureaucratic torpor to action, but it was effective in forstalling any action by the U.S. BTW, the assessment merely asserted that Iran had ceased work on weapons design, not that they had ceased uranium enrichment. It could just as well have been read to conclude that they had settled on a design and were just waiting to accumulate enough fissile material.
Although politically driven, the NIE was based on intelligence from Amiri, whom the CIA had rated as solid gold reliable.