According to wiki it appears the remaining Soviet stores of VX are still highly dangerous, a new plant was built in 2009 to destroy the last of it, so it probably has a shelf life of at least 20 years.
“Calling Hans Blix, calling Mr. Hans Blix, please report to the nearest red phone. We need to check your work product ASAP.”
I think Blix got eaten by a shark in North Korea circa 2004