Exchange of BDA Site Allotment

Hello Sir, I am planning to buy an individual and newly constructed house built on a site Area of 25 * 40 sqft (1000 sqft) in one of the popular locality of Bangalore. The seller of this newly constructed house bought the site from the Original Allottee in the Year 2011. The present site with dimensions 25 * 40 sqft on which the newly constructed house is built, was actually allotted to the Original Allottee by BDA in the year 2001, in exchange of a site with dimensions of 20 * 30 sqft (600 sqft) which has smaller dimensions than the present site (1000 sqft) on which house is built. so, My Question is, 1. Is it legally possible for BDA to allot a site of higher dimensions (1000 sqft) in exchange of original site (600 sqft) which was initially allotted to Original Allottee ? 2. How do I verify if the present site (1000 sqft) that was allotted to Original Allottee in exchange of previous site of smaller dimensions(600 sqft), is genuine and on what basis this exchange of site has happened to the Original Allottee ? Thanks in Advance.