This discussion clarifies the start date for claiming indexation benefits on long-term capital gains from property sales. The consensus is that indexation can be claimed from the date of each payment made, including advance payments, not just the final purchase deed date. This means if you paid an advance in an earlier year, you can benefit from indexation starting from that year.
Indexation benefit will be available to you on every payment made, i.e, if you have paid advance in 2010, that advance money will be indexed with index no. of 2010 and so on.