Cost of improvement tobe added in indexed cost of valuartion

I SOLD PROPERTY ON 08/05/2015. After keeping proceeds for stipulated period I am on my way to pay tax.While calculating taxable property,in indexed cost of valuar based price ,I added improvement cost ,viz.addition of stairs in [deleted]/,changes and additions in house at the time of shifting in house on retirement of husband from Govt, house to this house 200000/ in 1996-97, STRUCTURAL CHANGE & FOR LIFT &FIXING TOILETS PRIOR TO LETTING OUT TO MULTI NATIONAL IN 2007-08& incurred expenditure of 400000/ evidenced with bank witdrawals. I have evidences only in the form of withdrawals from bank. SINCE IT WAS NEVER FORESEEN THAT PROPERTY BE SOLD ,THUS NO DOCUMENTS KEPT.during the period ,as property was letted out but tenant left in between.& papers related to tenants were destroyed on shifting from one flat in to another flat,as never foresee need of documents as there was no plan to sell the property.In old house repair,additions are done with papers more than say seven years old not kept.,accepting evidences ,with affidavit be enough to accept by deptt. I submitted that a pragmatic approach in old bldg sale is to withdrawals plus affidavit/undertaking