Query lcgt

Case details :- My Father purchased a plot (residential) in Haryana in the year 2000. He paid the amount to HUDA (Haryana Urban Development Authority) in installments and along with that he paid extension fee (penalty for not doing the bare minimum construction), enhancement fee (HUDA has the right to ask for enhanced price twice as per demand raised by the previous land owners/farmers) Thus, Purchase cost + Cost of boundary construction + extension fee + enhancement fee = He paid a total of 11 Lakhs till March 2018. Now he has sold the land for 42 Lakhs and thus I have the below queries:- 1. He has to invest 42-11 = 31 Lakhs to avail LCGT or the complete amount of 42 Lakhs. 2. There is a ready to move in flat in Noida which I am planning to buy with my Father as a co-applicant. The builder has dues pending towards Noida authority and thus the registries are not being done for this society as of now (only possession letter issued and not even a single registry done till date). For thus, the residents who are living here for more than 5 years have filed a case in Supreme court and the court has now directed another builder to take over this society and complete the pending work. This is still not started and don't know how many years this will take. My query is, that when there is no registry done (and not sure that will be done in next 4-5 years) and that only the name transfer will be done in Builder's records and then in Noida authority's records and we will get possession of the flat, will my father be able to get capital gain tax benefit on this basis the payment transactions he would make from bank or registry of the flat we purchase is a mandate for that? The reason why we want to purchase this flat is that as there are no registries done and that a few towers in the society are not completed , the rates are low and we'll get it a bit cheaper than nearby societies. But with that capital gain tax benefit on the plot my father sold is also very important for us.