That is not completely true. I am a Campus Rep at my school and had a long talk with my Recruiter about PI's and she recruits in my area for both CP and PI's so she does see who applies for both and all that. She won't handle my application for PI because she already knows me and she wanted to step put but she does see both for everyone.
I also did find out though, because I am applying for both CP and PI, that once you have been offered a position for CP, that spot is being held. You do not need to respond to that until you find out about the PI. Your spot will still be available at CP. That is exactly what she told me to do. Apply for CP early, get my acceptance, hold onto it until I find out about PI's then make a decision. The idea of deciding to accept CP and then changing your mind because of PI is not right. You have then taken a spot from someone else that maybe didn't get the job because of filling job quota. I think its wrong.