Can different amount be mentioned in Sale deed and assignment deed? Which will be considered while LTCG calculation?

Sale / transfer of unregistered flat Hi, I have a flat for which all payments are done to builder but its not yet registered. I am looking to sale this property and I have found a buyer as well.The buyer would need to go for a home loan. I would like to understand the complete process and any tax liability. I understand, I will need to go for a assignment agreement (or probably this is what is called a tripartite agreement between me, builder and the buyer. I will pay the transfer charges which is 4% + GST. This agreement ideally is expected to be registered - is that correct? Since the buyer is going for a home loan... I would like to understand when the bank will be making the payment to me. Is it when the assignment agreement is going to be re-gistered, or is it when the property is going to be registered by the builder on the name of the buyer? Or will it be before the property registration but after the assignment agreement registration? From Tax perspective, I am selling the property at a very marginal difference compared to my total cost (which is total consideration in sale deed with builder+ amenities charges + water and electricity charges + car park charges and GST + transfer charges). Will my tax liability be based on this total cost... or it will only be based on the value mentioned in existing sale deed with builder. Would appreciate the clarification and details on this. Many Thanks.