Yes you are absolutely right. There was disconnect in understanding of my broker. He was expecting me to have a demat account with him and give him the POA so that he could debit the securities on settlement day. In that case no DIS is required and I need not be worries about the settlement number.
What I was referring to (eventually now that I understand) is selling with broker when my securities are held with another DP. (where I have to fill the DIS after sell and submit it to DP for debit to broker account for settlement)
Thanks for your help. It’s very clear now.