I retook my entire AS history year but only the actual exams, not the lessons, in my last year of college while still continuing it to A2 in the same year alongside law & sociology at A2 as well so that's bs what you've been told. You can always retake exams and almost always you can retake the actual year with enrolling onto the same courses you didn't get good grades in.
There were like 3 people in my A2 law class, who were also attending the AS law classes as they enrolled onto it again due to getting bad grades for it in August 2015