Hello,

There occurs two cut-offs. One is for attending Advanced. Another is dependent on institute that admit you based on JEE Mains score. And yes it depends on many factors like the difficulty level of exam, number of candidates, caste etc. This cut-off varies every year. If you intend to get admitted to IITs, then you can go for Advanced or else you can go for admission with Mains score.

It is authority named JoSAA that admits students to IITs, NITs, IIITs, GFTIs. For all institutes except IITs Mains score is accepted. Each institutes release separate opening and closing ranks for admitting students.