Also, the bystander effect deals with the probability of any individual helping out. It's still possible that there are two forces at play here: the declining probability of any individual helping vs the increasing probability that someone in an ever-larger group will still help despite the individual effect. It might be the case that there is a critical value N of bystanders where the second effect overpowers the first one.
I doubt that as N increases the "network" effects are strong enough to overcome the chance that someone that will help, regardless of what the effect of "N-1" bystanders is, shows up.
The effect is informative regarding what to do when you need someone's help, though. Since the basis of the effect is the diffusion of responsibility, it helps to address a person directly when asking for help. Instead of asking whether anyone in the group can help with something, point to a particular person and ask them whether they can help. In this way, the refusal to help becomes explicit and people will be less likely do that. This is something I've observed from personal experience too.
I have done this, and it has helped in mitigating the bystander effect. It means that there is a relatively large amount of people in the population that know what to do when accidents occur. IMO this makes bystanders who have done such programs to help, since they know how valuable time is in a lot of these situations.
Since I have done this training, whenever there is an accident on the streets and I am nearby, I will go help because I know what to do. And am therefor more likely to take initiative.
So I wouldn't immediately say this discount would be correct. It could also mean that some mitigation against the bystander effect is working.
"circumstance in which a party can be held liable for failing to come to the rescue of another party who could face potential injury or death without being rescued"
https://en.wikipedia.org/wiki/July_12,_2007,_Baghdad_airstri...
In the mentioned Kitty Genovese incident the numbers were inflated and while it isn't mentioned here, there actually were police reports while it was happening.
They were just ignored until it was too late.
This is the reason why Good Samaritan law is being brought into effect across the world.