Was the first agreement registered?
If it was a registered agreement then it is required to be cancelled by executing a deed of cancellation
Also had you paid full stamp duty on the first agreement?
Pursuant to the cancellation you are required to apply for refund of duty from the Collector of Stamps within the stipulated period
I am assuming that the first unit and the ground floor unit have same carpet area and except the floor all other configurations are the same
Also before signing the fresh builder buyer agreement did you even check and read the contents of the agreement?
Did you again pay stamp duty on the second agreement and was it registered?
All the above would determine whether you are entitled to claim compensation for delay
The exchange could not be done by any addendum
Because the stamp duty would be different depending on the market value of the units in 2011 and 2015
This was not any inadvertent error or any fresh terms agreed between the parties which could be recorded by an addendum
This was about allotment of unit as per the choice exercised by the buyer
So first the 11th floor flat was allotted to you and later you agreed to take the ground floor flat
So for proper conferment of title on you the new BBA was required to be executed simultaneously with cancellation of the first agreement
You have signed the second agreement. It will be presumed that you understood the terms of it and except the blanket consents and other clauses not in accordance with law, the other terms regarding the date of allotment would be binding on you and now you cannot claim that the possession date as promised on the first agreement is applicable
However outside of the second agreement if you have any correspondence with the builder prior to signing the second agreement in which the builder states that the earlier possession date will apply, then there is some hope. But even then the builder can say that upon signing the second agreement that correspondence was superseded.
So you ought to have carefully gone through the terms of the second agreement before signing and not simply and mechanically signed the agreement as given to you by the builder
It will be very difficult to lay a claim before Rera now after you signed the second agreement which constitutes a fresh contract between you and the builder and supersedes the obligations of the builder under the first agreement