I don't think anyone can proved you wrong because you are right but you can't defend your case in front of FPSC they 'll prove you wrong by just stating the clause mentioned above regarding condition about the failed candidates. You should be in patience and accept it by considering it Allah will and move forward for next attempt with full preparation.

Although I am following CSS from a long time ago and the general thought came into every mind that one should need to pass all courses and 50 percent aggregate as its the most competitive exams. The candidates you mentioned above who are serving are lucky or may be some persuasive factor.