sub registrar office for property

It is not clear what is your fact situation.  Without knowing the fact situation, it is not possible to give any answer to your query.

They are responsible for safety and preservation of all registered documents.  If your question is on  verification / Authenticity of earlier link deeds connected with such sale deeds referred in Present /disputed sale deeds, Certainly it is never responsibility of Sub-Registrar.

Buyer Beware is the law applicable in every case.  Sub-Registrar's responsibility is confined to only collection of correct Registration fees and that the deed contains main stipulations without ambiguity, which is different from verification/authenticity..  Sub registrar is concerned only with format of such deed alone.

(Realizing this flaw, some state governments like AP, has created a website and any citizen can have access to EC and sale deeds on line, and the system shall not permit those Government and other properties where registration is not permitted)