If the explosives were looted, why haven’t they been used?

Another aspect of the NYT story that, logically, doesn’t hold up for me is if the explosives were looted by terrorists, why haven’t they been used yet?
Note the following in latest MSNBC story:
“But other Pentagon officials, also speaking on condition of anonymity, suggested that the explosives could have been hidden elsewhere before the war. They also stressed that there is no evidence HMX or RDX have been used against coalition forces in Iraq.”
My assumption — and I’d appreciate if those who know such things would verify or correct me on this — is that if these particular explosives were used in Iraq, then the U.S. military would be well aware of it. I assume that they spend quite a bit of time and energy analyzing the methods and means of attack which the terrorists are using against us, and that if this particularly potent type of explosive was used, the techniques and technology are available which would lead to it being identified.
So if these assumptions are correct: how plausible is it that eighteen months after these explosives were allegedly looted by terrorists now locked in a life-and-death struggle with Iraqi and U.S. forces, none of the 380 tons of explosives have been used?
If terrorist groups did indeed loot it, and they have it, what could they possibly be saving it for?