i used active maths 1-ordinary level which we used in 1st and 2nd year and in 3rd year we just started higher level -active maths 2.
i have the same maths book and i wondering that myself but if you look in the chapter contents of the first book there's some chapters that are not in the higher lever book, so i'd say just look over them because for all the other chapters in the second book have a reminder of what you did in the first book
Hoped this helped
Only if you're thinking of dropping down to pass... Dont focus on it too much.. Stick to the HL as much as possible