books for GCSE REVISION from CGP

Hi guys I bought some books for GCSE REVISION from CGP for my exams and now that I'm resitting them when I checked if the books were still the same I mean the content inside I noticed some pages being different and the number of pages increased I'm not sure whether to keep the old ones or buy the new ones as my ones say at the end of the front cover FOR ALL GCSE ENGLISH COURSES - INCLUDING THE NEW EXAMS FROM 2017....>>> IM SCARED AND CONFUSED BECAUSE I DONT WANNA STUDY CONTENT WHICH IS OLD AS IM RE-SITTING AS A PRIVATE CANDIDATE AND I DONT WANNA MISS ON ANYTHING OR MAKE ANY MISTAKE AS IM LOOKING FOR HIGH GRADES
HELP