Buying Property in resale (Flat) with Exchange deed by First owner.

Hi, I am buying a property in resale (flat), the concern is that the owner does not have original exchange deed of the property. The owner sold his land to developer and both parties executed exchange deed in which it was mentioned that the developer is in-return selling flat to the seller in form of exchange with the land. Now I am purchasing the concerned flat from the current owner, but the original exchange deed is with developer as he needs it for his land CLU and other process. I have been given true certified copy of exchange deed in which it is clearly mentioned that the flat in concern has been sold to the current owner with full rights, ownership etc. My query is that, i will be executing sale deed with current owner but will not get original exchange deed. I would be getting all other original documents like BBA, Possession letter, receipts etc. 1. What documents i still need to ask for from the owner. 2. Will i face challenge in selling the property in near future as I do not have original mother deed (Exchange deed). 3. Any specific requirements in this case. Regards