Can exchange deed prepared and registered 20 years after verbal exchange

My grandfather were 4 brothers . The eldest brother had expired before 1989 and his son was his legal heir during this partition. In 1989 through partition all four took agreed shares and property was divided . However my grandfather (x) and son of eldest ( say y) ( late ) brother of my grandfather continued to do farming together on the agricultural land. The partition deed had each plot divided 50% between them. In 1997 my grandfather and Y decided to do farming separately. However unlike partition deed which had plot wise division equally , they verbally agreed for lot size . however in land records the mutation was in name of both in each plot . Meanwhile after 1997 Y sold few plots ( which had 50 % our share also which he sold without any signature or knowledge of my father grandfather or me ) through sale deed stating he is selling his share of land Recieved through partition . My grandfather expired in 2005 . My father who was working in a different city post retirement went to get the land mutated in his name in 2006 . While calculating he found that visa vis the partition deed which had each plot wise equal share here the land area after verbally exchanging it to lot wise is coming lesser by 13.5 dismil in our share then what it should have been in partition deed. He raised this . Then mr Y shared one sale deed of land purchased in 2000 which had total area of 21 dismil and was lesser value land . This was having 1st name as my grandfather and in between on page there was his ( Y) name also. Even if we consider his share of 10.5 dismil still it was short by by 3 dismil . But my father just to settle things amicably did not object . Also dismil land was in continuity and adjacent to our share of ancestral plot which we had it after verbal exchange done in 1997. So my father and mr Y went to CO block office. Prepared the affidavit and schedule of plots which was lot wise unlike plot wise in partition deed of 1989. It also had 21 dismil purchased in 2000 through registered sale deed in name of my grandfather but had name of y also in one place in deed. Entire 21 dismil was put in my father share to adjust 13.5 dismil he sold from my ancestral land. Through this revised schedule and affidavit in 2007 . It was submitted to block. CO issued an order in 2007 and lands got mutated respectively to my father and him respectively. Now in 2020 Y legal heirs are coming and showing the registered deed of that 21 dismil which has name mentioned of mr Y and claiming his share. Not only that they are saying that schedule of 2007 has lesser land in name of y without accounting for fact that y and them sold our share of ancestral division without consent . They were trying to confuse villagers . We went to village and when we sat in front of panch they could not convince and agreed. Pls advise can we make exchange deed retrospective and get registerd now . What can be permanent solution.