I took the exam with 2 classmates. I know that there were at least 2 patient models that the 3 of us put different differentials and plans on. We all passed.
I think there are probably a set of acceptable differentials/plans for some of the patients. As long as you're within those, I think you're fine. I'm assuming there are patients where they expect you to be on a specific wavelength and take your differential/plan in a certain direction.
All guesses/suppositions as I'm not involved in the testing, but I can at least confirm that you can get a different answer from someone else and still have both pass.