OPCW tests link Syrian government Sarin to the August 21st 2013 attacks in Damascus, and the Khan al Assal attacks. The Syrian government has denied losing control of their chemical weapons stockpile. af.reuters.com/article/worldN…
As I wrote in November last year, OPCW reports on the 2017 Sarin attacks showed the chemical markers the OPCW used to connect the Sarin used to the Syrian government were also detected in sales from August 21st 2013 bellingcat.com/news/mena/2017…
Also, more people continue to own @DanKaszeta an apology over claims he was wrong about hexamine. This is why you don't use rabidly pro-Assad chemistry students as your chemistry experts, Ted Postol. 
Keep in mind Russia created a dossier showing rebels were responsible for the Khan al-Assal attack, which is now chemically linked to the Syrian government's stockpile. I called out their dodgy dossier way back in 2014 thedailybeast.com/its-time-russi…
Of course, if Russia really wants to insist its dodgy chemical weapons dossier is proof rebel groups were responsible, they could make it public. They even claimed to be able to ID the exact rebel rocket used, so are they telling the truth, or are they just lying? Can you guess?
You can read the various articles I've written on Sarin use in Syria here bellingcat.com/?s=sarin
