Response:

Making this finding requires proving a negative and the IAEA has set a very high bar for doing so.  The Lawyer’s Committee on Nuclear Policy reported in 2006 that the IAEA applies the same “unable to conclude” status to every country that had not accepted the Additional Protocol at that time, and to 40 nations that have accepted it.  

This does not mean that Iran's conduct is no more worrisome than the conduct of other countries.  It clearly is much more worrisome.   The point is simply that lack of proof of innocence is not the same thing as proof of guilt, and a lack of an IAEA declaration of "no undeclared nuclear materials or activities" is not terribly probative in an of itself.  The IAEA has declared, repeatedly, that it has found no evidence of Iranian diversion of nuclear material for illicit purposes.