Dc conversion certificate required for land on bbmp approved

We are looking to buy an apartment at a gated community in Bangalore which has OC received, A Khatha and is RERA approved. On going through the documents, the land seems have to be converted from Agriculture to Industrial 40 years back. The area has now been classified as a Residential Zone by BBMP. Is a DC conversion order to Residential required for this land? The owner is saying that since BBMP has approved the project and the area is classified as Residential, the conversion order is not required. Please advise.