Those are commentaries . . Mostly basic concepts are from NCERT. . .it's good for basics as well as many direct questions have been observed . . Obviously not all questions can be expected from a single source. . but basic ncert should be mastered. . So that such questions are accurately attempted. . .
but sometimes upsc selects questions from advance books like upender singh or other writers thats not under ncert , how that can be explained ?
Those are commentaries . . Mostly basic concepts are from NCERT. . .it's good for basics as well as many direct questions have been observed . . Obviously not all questions can be expected from a single source. . but basic ncert should be mastered. . So that such questions are accurately attempted. . .