That makes 5 nights of poisoning - 1 I escaped with the Ring, two more were healed with one-off PMs that were not on people's initial PMs, and Colin was killed before he could die from poisoning. Only Brendon actually died from being poisoned, and that on the evening after the final lynching.
I think maybe that made poisoning slightly too ineffective. It's not like the mafia had a lot of factors in their favour without that.