Now I Know it is not required to make a disclosure for a disease that happened after taking the policy

But Niva Bupa ReAssure Has a line that says

8.17. Disclosures on Renewal: You shall make full disclosure to Us in writing of any material change in the health condition or geographical location of any Insured Person at the time of seeking Renewal of this Policy, irrespective of any claim arising or made. The terms and conditions of the existing Policy will not be altered

which one is true even though it says the policy will not be altered

and Can they deny the claim even if I did not make the disclosure at the renewal