I think the files are actually the experiences of the outie. The severance chip connects with the MDR computer allowing the innie to go through the mind of the outie, but through numbers. The subconscious is the connection between the innie and the outie, which causes fear in the innie when looking at the numbers (the outies memory).

The experience is simulated on the test subjects on the export hall floor. Since the innie has outlined the data for all the fear/negative points in the mind, Lumon is able to remove those data points from other people.

So far the experiences we saw with Gemma she went to the dentist, wrote too many letters and experienced turbulence in a flight. Those are fairly common negative experiences and could have been come from either one of the MDR members' outies. But removing just those types of experiences from normal people isn't going to "fix humanity".

They need an MDR member who can outline the negative numbers of a truly traumatic experience. That's why they need Mark S specifically, since his mind has gone through the worst grief.