hi mohit,
If any one purchase immovable property in less prise then the stamp valuation then no tax liability arise at that time but when he sale the property in future while calculating indexation then calculation must be on purchase price so the valuation goes down and tax goes up
Ex on 1991 stamp value of x property is 500000 but i purchase in 300000 and sold it in 2012 in 2500000 lac.
So while computation of index
(852/182)*300000=1404395 then my LTCG is 2500000-1404395 =1095604*.20 =219120
(852/182)*500000=2340659 then my LTCG is 2500000-2340659 =159341*.20 =31868
Now u clearly show the difference in future tax