To look at this another way...
How many shells were looked at by both our people and the UN and assumed to be HE, but are actually chemical weapons? Unless you actually take the shell apart or weigh it, there is no way to tell. A visual inspection isn't enough.
Something to think about, Mr. Blix, eh?
I lost any tiny sliver of confidence in the UN inspection teams when I saw the video of them right after they found an empty WMD artillery shell. They had on no chemical gear, gloves, goggles, nothing. They were peeping inside the hollow shell and running their hands along it. At the time they had no idea if there was any residual nerve agent in it.
Morons.