Sale agreement misplaced and unregistered

I want to buy flat in a society older more than 30 years. It was created by trust and then transferred to current society. All the first owner get share certificate from society and no agreement was executed at that time. Although, I have to buy a property from 2nd owner who has purchased property in 1988 from 1st owner. However, he misplaced the sale agreement. Also, such agreement is not registered. For misplaced of agreement, owner has field FIR and gave the advertisement in local newspaper. Now conclusive proof is share certificate available with owner. Society has OC and conveyance both. I cross check with few banks for loan purpose and verbally they willing to provide the loan. Considering above, Is there any legal liability on me in future if I decide to buy such property even my sales agreement will get registered with 2nd owner? What will be the risk which I am carrying at present and in future, if any Can titile of such property considered as clear or it is defective?