Correction of GPA number in an old sale deed

I was planning to buy a plot. This plot was owned by Mr. A. and he was allotted it by the builder. Mr. A has given a GPA to Mr. B giving him absolute rights of the plot GPA was registered under number XYZ. Mr. A also executed a will favouring Mr. B and also given an affidavit that this GPA is irrevocable. This GPA was executed with the builder also. Mr. B sold the plot in 1998 to Mr. C through a sale deed but while selling this plot the GPA reference number has been mentioned inadvertently incorrect. The last numeral has been mentioned as 7 instead of 1. It is the only sale deed in which the reference to GPA is given. Mr. C then sold it to D and Mr. D sold it to Mr. E and nobody noticed this error. Mr. C is traceable and may support in rectification but Mr. B is not traceable. Mr. A is also not traceable. a) I am not sure how to correct this GPA number in the old sale deed of 1998. What are the options for me as I have already paid 10% advance to the seller E? b) If we get the notorized copy of wrongly mentioned GPA (number) then can it help? Because it will indicate to some other thing. Please suggest a wayout.