Mismatch in layout plan and sale deed measurements

Hi, My relative got a property from her father by way of a compromise petition (final decree not done as no one was aware it had to be done) from her father in the civil court. She got the property registered in her name way back in 1994 with the order of compromise petition which she received from the court and the property was registered to her name by the Sub-registrar, she only had the compromise petition from the court as her basis of the site measurements and she was not privy to any other information regarding the site from her father. Nevertheless, the site got registered in her name and she got the khatha transferred as well, no obections from anyone whatsoever. She sold the property to a person and he got the property registered in his name and all the work was done, within the same year he transferred the property to his son (gift deed in 1995) via a gift deed. Now after more than 25 years he has got some documents saying that the property in the mother deed, the site measurements are less than the measurements mentioned in the compromise petition mentioned as per the courts direction. Now since my relative nor the initial buyers son were never aware of this document. What can my relative do in this case? She had made the sale back in 1994 and had handed over the possession of the property as any sale deed takes place. Now he is coming back after 25 years saying that there is a mistake and that my relative has to fix it. He has already put up boundary walls as per the gift deed and has been in possession of the property without any problem. Can someone please suggest what can be done to help my relative?