Re: Bude
"If they were the target and they were attacked at home (as you describe) they would have not been alive. "
-- Voland's right hand
They very, very nearly were not alive. It doesn't matter how lethal a poison is, if the dose is low enough and/or medical attention prompt enough, there are circumstances in which a victim can survive. That's why measures like LD50 have to be used, after all.
In any chemical attack, the injured outnumber the killed. Tokyo subway sarin attack, about 50 dead, hundreds severely affected, thousands affected overall. Hell, it's probably true in any attack (with the exception of airplane bombings or other 'traps'): in the Manchester Arena bombing the ratio of injuries to fatalities was over twenty to one. Are you going to argue that bombs clearly aren't lethal, because most of the people injured weren't killed? No: even a lethal bomb has a non lethal 'dose'.
A potent nerve agent is a f***ing stupid assassination weapon. The only way to be sure to kill the target would be to use a dosage that would cause huge collateral damage and contrariwise, a precise dose is not guaranteed to kill (moisture in the environment hydrolyzing the compounds; other environmental effects; skin absorption variability; genetic differences in susceptibility due to PON1 or other enzyme differences; promptness of medical attention; etc., etc. --- just too many factors to make it suitable).
So why use CWs? To send a message. That message is "the Russians did it" whether or not the Russians actually did do it. But, on the balance of probabilities, the Russians did it. It's the old horses-head-in-the-bed: the signature is completely obvious to everyone without being anything like evidence.