Validity of Sale Deed executed thru an unregistered GPA

Am intending to buy a property in the state of Tamilnadu, which was bought by the current owner in year 2004 through a Sale Deed executed by attorney under GPA. The GPA was not registered with Sub-Registrar but duly notarised. I was told that the requirement to register a GPA with Sub-Registrar was not compulsory in 2004 and notarisation is good enough for the document. Whereas I read in some articles that power of attorney is in respect of an immovable property of value more than Rs100 is a must for its validity. Kindly advise. Also, I have been told that the notarization should carry the Serial Number and Page No. of Notarial Register, and Notarial Stamp for a minimum of Rs.10/- in addition to Notaries Stamp, his/her name and signature for the notarization to be valid. In my case first 2 items are not present and it carries only Rs.5/- stamp (Note the Notarisation was done in November/December 2004). Kindly advise. Also, kindly advise whether any remedial measure(s) / correction to the above exists.