The IAEA has a response to that point:
ABC said the inspection report noted that the seals at Al-Qaqaa may have been useless because the storage bunkers had ventilation slats on the sides that could have been removed to give looters access to the explosives.
But Fleming said the inspectors had also checked the ventilation slats to ensure they had not been tampered with, and that they concluded "the confinement was sufficient" as long as the site was regularly checked. They could no longer do that once they pulled out just before the invasion.
http://www.chron.com/cs/CDA/printstory.mpl/world/2871177
According to the above, IAEA spokesman Fleming says they could tell if the vents got breached.
I'd like more details on that. See if David Blaine could fool the IAEA, and get in through the vents without detection.
The U.N. inspectors also clearly said that they insptected, "some, not all", of the vents/shafts in the sealed bunkers before they left. What does 'some, not all', mean? One? Two? fifteen? In any case, they admit that when they left they had no idea whether or not some of the bunkers had been entered through the vent shafts.