Important legal context: the origin of this Geneva ban is not only that gas weapons are atrocious, but that your foe might doesn’t know what gas has been fired and may reply to CS with gnarlier chemical weapons. The treaty also names the issue that the offending forces may, inadvertently or perfidiously, not know or mix up what gas they’re sending downrange.
This is a big fuckin’ deal in the current conflict. Russia uses a near-identical gas grenade for both CS and nerve gas, in Soviet era crates and stockpiles handled by the hard-luck HIMARS catchers in their logistics chain. If they fuck that up or a pissed off Buryat conscript wants vengeance via sabotage, a whiff of bad-boy gas on the wrong wind could make things extremely spicy.