To date, all nerve agents used in the Syrian conflict have been binary chemical warfare agents, so-named because they are mixed from several different components within a few days of use. For example, binary Sarin is made by combining isopropyl alcohol with methylphosphonyl difluoride, usually with some kind of additive to deal with the residual acid produced.  This is to make handling and storage safer. Once mixed, the residual hydrogen fluoride acid breaks down anything the Sarin is stored in and it quickly degrades .   

Dropping a bomb on the binary components does not actually provide the correct mechanism for making  a Sarin cloud. Since one of the precursors for Sarin is isopropyl alcohol, it would go up in a very large ball of flame. Yet none was observed by either side. 

Another issue is that, if the Syrian regime actually did believe that the warehouse stored chemical warfare agents, then striking it deliberately was an act of chemical warfare by proxy.