It was about 13 years ago. Recall that the famous 2007 NIE followed a similar deep dive.
From the UK Iraq Inquiry a few years back:
TIM DOWSE: Although it was unusual then, it has become notquite standard practice, but much more common since,because we did, partly as a result of the Butler Review,establish a challenge team, and there were a series ofpapers over the next few years, none of them relevant toIraq,where we reviewed our judgements.We conducted a very major review,on the Iranian nuclearprogramme in, I think, 2006. That was, for fairly obviousreasons, because of the Iraqi experience. We wanted tolook at it, take a completely fresh look, and say: is thisreally for a military purpose?