that's what i'm asking i have non-creamy layer certificate of obc issued in 2016 and valid for 3 years upto 2019 but they are asking certificate of 2017-2018

I would like to tell you that the the income limit was increased in Sept. 2017 for non-creamy layer category. As per your saying, non-creamy layer certificate of obc issued for you in 2016 has validity of 3 years i.e. upto 2019, it foresees that you'll remain NCL candidate for next three years. In such scenario, it'll be imoprtant to watch how the DU officials see at it.