Cassiopeia - Aspect of the Serpent - Problem with stacks

I know this is late, but I haven't play Cass in quite a while.

Location - Twisted Tree Line (During the Harrowing Event)

Problem - Her new passive isn't counting the number of stacks from her poison properly. I don't know if its lack of clarity or a real bug

Info Provided - Cassiopeia gains a stack of Aspect of the Serpent for each second that an enemy champion is poisoned, for each poisoned unit that she kills and when she hits an enemy champion with Twin Fang, up to a max. of 400 stacks.

My Thoughts - According to this, poisoning a champ gets a stack of Aspect of the Serpent. So what happens when I poison more than one champ at the same time? I got this equation; ( Current stacks ) = ( Current stacks ) + ( the number of champs poisoned * duration of poison ).

Clarity - Please change the info provided to state whether or not poisoning more than one champ gives Cass 1 or more stacks

Please respond to any mistakes I have made regarding this issue.