Calculation of ltcg-sale of property

I have a property in Gurgaon, which was purchased in FY 1995-96. I paid an amount of around 44 lacs.

I now wish to dispose of the property and expect to receive about Rs 2.5 cr. As per my knowledge, the LTCG is to calculated as under

     Sale price - indexed value of purchase price on date of sale (say FY 2019-20)

     ie 2.5 cr - ( 44 lac x ( index  yr 2019 - index yr 1995)

However, I have been informed that for property in Gurgaon, I need to have the property assessed to determine its value in FY 2001 and thereafter calculate its present value by multiplying the assessed value by (index in 2019-20 - index in 2001-02)

I am unable to understand the need to have the property value assessed as above since I have exact details of purchase cost.

Could someone kindly clarify and explain how I have to calculate the LTCG.

Thanks