Interesting wording. I believe only mustard nerve agent degrades, while sarin is still as potent as it was when made.
Efforts to Lengthen Shelf Life
# According to the CIA, nations such as Iraq have tried to overcome the problem of sarin's short shelf life in two ways: The shelf life of unitary (i.e., pure) sarin may be lengthened by increasing the purity of the precursor and intermediate chemicals and refining the production process.
# Developing binary chemical weapons, where the two precursor chemicals are stored separately in the same Shell (projectile)|shell, and mixed to form the agent immediately before or when the shell is in flight. This approach has the dual benefit of making the issue of shelf life irrelevant and greatly increasing the safety of sarin munitions