Registration alone would probably not have prevented it completely. However, it may be the reason why, unlike what happened with Marc Lépine, far fewer people were harmed by Kimveer Gill, because the police were able to respond very quickly.
When we talk about prevention, we are not talking about eradication. We are logical enough to understand that the gun control system is a method of prevention. So, it is difficult to develop figures for things that never happened. However, the numbers we have at this time show that there has been an improvement in people's quality of life—there are fewer murders and there is less domestic violence. The figures are clear. You obviously cannot count incidents that never happened.