Typo in Sale Deed Document no. mentioned in Settlement Deed.

A Sale Deed was made for residential plot in 1972. The Purchaser gave the land to her sister by way of Settlement Deed in 1985. The purchaser passed away in 2008. Her husband is alive. She had no issues. The settlee, now tries to sell the land. It is noticed that there is a typographical error in the Sale Deed Document no. mentioned in the Settlement Deed. Extra one digit has been added to the Doc. no. For eg., instead of 1654/1972, it was mentioned as 16458/1972. All the other details of the sale deed are mentioned correctly. 1. As the Settlor is no more, how to rectify the Settlement Deed? 2. Is there no need to rectify it, as 30 years have lapsed since the settlement deed was executed? 3. Whether the Settlee can execute an Affidavit saying there was typo in the Settlement Deed and register this Affidavit, so that it is reflected in the EC and Will that suffice to have correct title? 4. I intend to buy the property. Will the title given to me be clear? Will there not be any issue when I resell? - Raj