: You can file an RTI request with the Department of Registration and Stamps to formally request specific 2001 rate data for your locality.

: Approximately on built-up area (BUA).

: By using the 2001 rate instead of your actual (likely much lower) 1980s or 90s purchase price, you increase your "base cost," which lowers your taxable gains. How to Find Mumbai RR Rates for 2001 (Free & Paid)