Rectification of in covered area in old sale deed

I purchased a 3bhk Flat in Ashiana Utsav Bhiwadi on 25/08/2014 .It was third resale of this Flat. Aftter getting it registered in my name I cam to know that covered Area of this Falt is only 1420 sq.ft and not 1480 as mentioned in the sale deed.When enquired from the seller he told that he too purchased that in 2013 as h1480 sq ft from first owner.On checking the first deed it is found that at the inception and fist stage the covered Area of this Falt was mentioned 1480 sq instead of 1420 sq ft by mistake and error of Ashiana Housing Ltd while drafting the first sale deed to its first purchaser Mrs.Ruch Gupta and it was not pointed/find out by any one before. This Flat was sold to Mrs Ruchi Gupta by Ashiana Housing Ltd in 2010 as covered Area 1480 sq ft. In 2013 this Flat was Sold to Mr.Babu Lal Sharma by the Father in law of Mrs.Ruchi Gupta on power of attorney mentioning again 1480 sq ft. In 2014 this Flat was sold to me by Mr.Babu Lal Sharma to me again by showing 1480 sq ft. After getting possession I found that this Flat is Tulsi 2 with 1420 sq ft and not Tulsi 1 which have 1480 sq.ft. On clarification Ashiana Housing Ltd accepted and confirmed that actually covered Area of this Flat is 1420 sq ft and not 1480 as wrongly mentioned 1480 sq ft by mistake in first sale deed executed by Ashiana Housing Ltd and Mrs.Ruchi Gupta in 2010.No comparison with relevant record was done that time.The allotment is for 1420 sq ft and reportedly they charged for 1420 sq ft in first sale. Sadly the first owner to whom Ashiana Housing sold this Flat in 2010 has expired .This Flat was resold to Babu Lal Shrma in 2013 by her Father-in Lal on power of attorney and this mistake of covered Area continued further up to third sale deed . Please advise how tis error/mistake can be rectified now ? Who is required to process the rectified deed ? Who is required to sign the rectified deed on behalf of late Mrs.Ruchi Gupta first ower? What will be the payment of registration and stamp charges for this rectification deed? Who is required to pay the stamp/registration charges on this error/fault for this rectification deed.