Release Letter from Bank

I want to explain the situation as follows: Rajesh bought flat from Suresh in a XYZ society located in Greater Noida. Suresh bought the house from the builder directly with his own cash and no loan in 2011. Rajesh purchased the flat in 2018 with National bank loan . The registry is done between Rajesh and Suresh and before that between Suresh and the builder. Now after the loan disbursement , National bank asked for a release letter which is not available with Rajesh or Suresh. Eventually the XYZ builder had mortgaged the society with State bank and for every sale they have to deposit the sale proceeds in the loan account. But as Suresh did not know about this state bank mortgage, he never asked for the release letter/ NOC for his specific flat and the builder also not gave it to him. Rajesh has been asking for the NOC from the builder and the bank. The builder states that since the registry is already done between Suresh and Rajesh, they are no longer liable and none of the other flat owners who has loan ever asked for such letter. When went to the bank, they asks for all the payment details made by Suresh and the letter from the builder stating where the funds were parked which the builder is not issuing. My question is does Rajesh really need this NoC from the bank? If he pay off all his due loan and closes the account , the national bank won't ask for the NoC but for the longer run in real practical life is this NOC/Release letter that much important? Rajesh has all original sale deeds, builder buyer agreements, allotment letter and all the necessary documents. Should Rajesh put all this effort for the NOC?