On discrimination in retake exams
I'm afraid that quoting external regulations and grading guidelines here won't do you any good. The question is what are your university's internal grading policies. Do they have a recommended grade distribution? Are there rules governing repeat examinations for students who had to miss the first one? Are there policies on what is allowed to be covered on such examinations?

Whether good or bad (and it's a bit of both), grading standards differ between institutions, and even within different departments at the same school, and sometimes even course to course. That means you can't rely on what others do to help, and you can't really claim "discrimination" here, either. Such policies are clearly unfair and unethical—it's not right to force a fixed percentage of students to fail, regardless of their actual performance. However, unless your university's regulations specifically forbid such behavior, there's not much you can do to fix this.