I for one never believed that it was a "false flag." It's pretty hard to fake drooling all over yourself and dying.
Even as we were entering Iraq during the first war there, the convoys of Saddam's material and supplies for making chemical weapons were headed to Syria. Saddam used the blister agent mustard gas and the nerve gas Tabun, and Syria inherited the materials and tech personnel to make that.
Apparently since then, they've opted for a much easier chemical weapon, mainly chlorine gas. Concentrated chlorine is much easier to produce, and easier to work with. That doesn't mean that they don't have other chemical agents though. The Syrians also have stocks of nerve agents such as VX, as well as blister agents like mustard gas.
The most noteworthy of the chemical weapons used during the Syrian war was sarin, which they've used on a number of occasions. They used that in 2017 during the Khan Sheikhoun assault, as well as attacks in 2013, including an attack on the Damascus suburbs which was thought to have killed 1,429 people.
