The reason for this is because, although i do not agree with their changes, the gcse exam boards are getting negative feedback in regards to the 'harshness of their marking', them accommodating only the 'most able students'. (Part i do agree with) Since the exam boards revolve around the standards of the typical population, usually public school student (most of which are average students), they have lowered the grade boundaries considerably. Fundamentally, when the boards believe that there are too little a stars or too many a stars the grade boundaries change, thus, the fluctuation.