Vel'Koz One For All

I have a question about Vel'Koz's passive in One For All. Obviously, my teammates and I can work together to stack it. But if, say, two people worked together to apply all three stacks, would it do double damage? (One 'completion' proc from each Velks), or would the three be consumed as one proc, regardless of who made it? I'm asking because our passive seems to do a lot more damage than it should. (Although to be fair, we were up against Sonas. So.)