The very question of misplacing or losing the documents create suspicion.
the issue is to be tackled very carefully.
There are chances that the owner mortgaging the property with any bank or a NBFC pledging the original title documents and afterwards on the basis of an application stating that he lost the original documents he might have procured the certified copy of the registered documents.
Evan an indemnity bond executed by landowner now to sell the property on the basis of certified copy of the registered title document may not be of any use in future because the landowner will not be bound by such unregistered document (indemnity bond) and will escape the responsibility.
Unregistered mortgage deed even with the bank cannot be traced so easily, the banks will offer loan on an equitable mortgage and do not register the property instead they mad register the memorandum of deposit of title deeds alone which will not reflect in EC.
Take a legal opinion from a local lawyer before venturing into the purchase of the property.