You are right that the UDR scheme commenced in the year 1985 in Tamilnadu, therefore it is not possible that the dead person would have applied for udr patta after his death.
This is a false and frivolous suit filed by the so called legal heirs only with intention to grab the property or to extort money as much as possible by creating false litigation.
The death certificate obtained now and the so called UDR records also can be challenged.
Before that you may have to confirm the status of the testator when the vendor sold you the property, i.e., when was the Will written, when did the original owner/propositus die and whether the vendor transferred the property to her name post death of the testator?
These information will be useful to you to handle the case properly.
The Panchayat President is not an authority to issue death certificate neither the VAO.
At this belated stage, the death certificate can be issued by the authorities competent or by a decree of declaration by court of law, hence it can be nullified when properly challenged.