Construction loan/LAP taken on plot by Builder, builder selling f

I am looking to purchase a builder floor in Gurgaon constructed on a plot by a small time builder. This builder has taken a loan on the plot of land from one NBFC/karvy finance for construction purposes. Now the builder is selling individual floors and would get me the the registry done for my floor. Now I am looking to take up a loan from another NBFC to purchase this floor. How does the things pan out in terms of getting a mortgage loan from another bank on just this floor when the whole plot of land is already mortgaged with another NBFC. Is this legally possible that the existing lender issues an NOC to allow the builder to sell one of the floors? The existing lender would still have the plot papers in it's custody as the full loan may not get paid off after a sale of just one floor. What paperwork is usually required from the existing lender. Like NOC, permission to mortgage, list of documents. How would my bank/HDFC verify the original papers in custody of the other lender. Please help. Thanks Regards Varun