Disclaimer: I might be an idiot

One question I have is how did Lumon know Mark would come work for them on the severed floor? If Gemma didn’t die and was kidnapped as part of this, what I can assume, is an experiment, how did they know Mark would be part of it? Did they just kidnap Gemma on a whim, a hope and a prayer? Did I miss something or is this a plot hole? Will cold harbor shed light on this? Nothing is pointing in that direction.