Because the syllabus is divided into volumes, minor overlap exists. For instance, Maxima and Minima appears in Calculus as well as briefly in Algebra under Quadratic equations. This is intentional for revision, but novices often feel they are repeating the same concept.
The JEE is unpredictable. One year the vector question is easy; the next year it is abstract. Cengage exposes you to of a problem. If you solve all the exercises in the Coordinate Geometry book, you will rarely encounter a "new" type of conic question in the actual exam. cengage maths for jee mains and advanced