"Four months?" Where have you been?
The CIA hasn't exactly been covering itself with glory for a long time now, and the list of things they've gotten wrong or been blindsided on is well known. Commenters also point out 9/11 and the collapse of the Soviet Union.
The reasons for these errors are complex and varied, and I'm willing to grant that a few were probably unavoidable by the very nature of the business.
Their position on Iran's nuclear program has been jerking around like a mechanical bull. Remember--this is their latest public position.