You only forgot to consider that there are still drivers in the cars, so each time the human intervene it could have prevented an accident , I am not sure what

You only forgot to consider that there are still drivers in the cars, so each time the human intervene it could have prevented an accident , I am not sure what is the average victims per accident say 2 , you can multiply it with the number of time the drivers had to take over and you have an upper limit, if you don't like this upper limit then we need better numbers but this companies keep them secret or under report the problems.