How to find the year of stamp paper

Dear distinguished members, Please help me to find out the veracity of a stamp paper worth of Rs. 50 as one of my cousin sisters appealed to the District Magistrate in April, 2018 to cancel the registration deed of agriculture land which was transferred to my father long ago (40 years back) through ancestral property from my grandfather. Now they have submitted a proof of agreement which was signed by my grandfather who was expired in 2010. The paper showing a stamp paper signed by my grandfather (which is clear forgery) on 04.04.2005 on the stamp paper bearing No. 00AA751964. Now my request is that can somebody guide me the procedure to deal with this situation. I am of the opinion that if I find out the year of issue of this stamp paper number I can show it as a proof to Collector that it is clearly fake. If any advice from dear members, please enlighten me. Regards Shravan