Plot purchase - missing buyers signature in the current sale deed

Dear Sirs\Madam Am planning to purchase a plot from a seller lets say Mr Shankar. Shankar actually has purchased this plot from one of builder in Bangalore (Ferns), that plot was bought & registered on both Mr. Shankar & His Mother, in the year Feb 2013. When we checked their Feb 2013 Sale deed, we noticed two things 1. In the last page where seller & buyers usually sign (along with witness).... we could see Sellers (Ferns) Signature, but on the buyers side it has only the signature of Shankar's Mother. Mr. Shankar DID NOT Sign the sale deed. 2. On all other pages only the signature of seller (ferns) is there. Both the buyers (Mr Shankar and his mother) signature is not there i other pages. What is the impact of this issue? How to Correct? regards, Arun