Power of attorney

I am purchasing a plot on the basis of Perpetual Lease from Co-operatve Housing society.The said plot was originally allotted to one Mr.(A) on 09.11.2013 and accordingly, a perpetual lease agreement was entered into by Housing Society and Mr.(A) on 09.11.2013.On 20.12.2017 an Irrevocable General Power of Attorney was issued by Mr.(A) in favour of Mr. (B) wherein it was mentioned that attorney holder can execute Perpetual Lease Deed or any other necessary document/Deeds (Except sale Deed) in respect of said property and also to transfer the lease hold rights of the said property and the executant cannot revoke/cancel the said attorney without the written consent of attorney holder, besides the other usual points. Now the problem is that the original Perpetual Lease Deed entered into between co-op hosing society and Mr.(A) is missing and is not now available. The GPOA holder Mr.(B)has transferred the lease hold rights of the plot to one Mr.(C) on the basis of GPOA and has been duly entered into along with the housing society on the basis of certified copy of perpetual lease dated 09.11.2013 obtained from the concerned court.Now I m purchasing the said plot from Mr.(C) on the basis of transfer of lease hold rights and certified copy of perpetual lease. However, co-op Housing Society has already acknowledged that the said plot is in the name of Mr.(C). Kindly advise me in the matter and also kindly guide me if any extra caution is be exercised. Thanks