Patta for grama natham in tiruvottriyur in chennai

Hi, my mother owns a property which was purchased by my grandfather back in 1960s. There was a factory that was also operational for a long time. My grandfather had given the same as settlement to my mother. The documents that we have are parent document, settlement deed etc. However, we don't have a patta instead we have a field register. In the field register few portions of the land states its gramma natham and few states its punjai. We are being told that we cannot get patta for the full extent instead we can only get patta for the non natham land. However in one of the articles which i read in one of the newspapers on december 26, 2018 it states that one can indeed get patta for grama natham land. if the land value is more than 7.5 lakhs then the same should be issued by the state government. Is the above mentioned obtainment of patta land correct. If so how do we go about getting the same. Kindly advise.