You mean claims, Nicky. Claims by Syrian air defence. Data is backed by evidence, claims are unsubstaniated statements.
The targets are supposed to be manufacturing and development not stockpikes. In order to actually destroy stockpiles of chemical agents like chemical weapons a specialised weapon type has to be used that is a FAE or Thermobaric warhead, and a large one at that. These weapons use the air around them to super heat the blast zone to considerable temperatures. The problem be is using those systems dramatically increase the potential for collateral damage. The size of warhead needed to take out a chemical weapons store is smaller than a small nuke but far more than the normal bomb loads.
And if the Blast doesn't kill everything around the location any residual Fuel air compound can be just as toxic. Additional the effects are nasty those in the blast zone are incinerated those around the edges are hit with large concussive force that can rupture internal organs.
It's a rather nasty way to go. ThatsT not to say that the US DOD doesn't have them they do but seem less enthusiastic regarding there deployment and depoyment options. By treaty FAE are not considered WMD IF IF used against military targets. Both the US and Russia have empoyed FAE in some infantry weapons like grenade launchers, mortars and shoulder fired recoiless both also have smaller bombs and missiles like the enhanced blast hellfire.
But for a warehouse loaded with WMD you need something of considerable higher magnitude. And if that warehouse is in a urban areas that means considerable potential for civilian death and maming. Why commit what is basically a war crime to prevent a war crime? It's one thing if the stocks are in the middle of a Army base another in central Damascus.
If those issues don't turn your stomach, there is the issue of delivery. The largest US FAE I know of is the BLU118/B based off the BLU109 gravity bomb. That means that delivery of the FAE would demand a bomber or fighter, the bomb is too large to carry in the weapons bay of a F22 or F35 so it would have to be a B2 or either F15E or F16. That would mean increased risk. Currently I am not aware of any stand off theobaric weapons (IE Cruise Missiles)