Who knows? The Hussein govt. claimed they destroyed the known stock of nerve gas following Gulf War I, but didn't document it or bother to follow any of the required inspection protocols. There have been a few binary chemical gas artillery rounds found with some of the gas (rounds they also weren't supposed to have had), but no large quantities. There was also a report out of Jordan of a foiled terrorist attack using poison gas. Allegedly, the terrorists were Syrian, but Syria has no reported manufacturing capability.
The amount missing and not Documented would show a HUGE corruption with in the government of Iraq at the time of the weapons turing up missing. To the point where in my opinion the government was about to fall anyway. Which is why Zarqawi said he was in Iraq, to take Iraq prior to 911.