Time Limit for Reinvestment Purpose - Capital Gain

To avail benefit under both the sections 82 and 86, the outer limit is 3 years for construction of residential property. I will be availing exemption under section 86 by redemption of mutual funds over four years as and when the installments to the developers. My query is whether I am right in claiming exemption for property u/s 86 even though I know before hand the project will be over only after 36 months from date of accrual of first capital gain. There is one view that it is enough if the required amount is reinvested within 3 years from respective redemption of mutual funds and completion criteria within 3 years from the date of first redemption of mutual funds will not be a problem in claiming exemption for each of the redemption.

I am aware of the case of Sambadam Udaykumar decided by Karnataka High Court that the assessee discharged his liability of reinvesting within 3 years by paying installment to the developer but the delay is caused by the developer. Hence, he is eligible for capital gain exemption. In my case I am well aware that it will not be over within 3 years from the date of first capital gain

I request experts to give their view on the above query.

I have another query how to arrive at 10 crore upper limit for claiming exemption prescribed u/s 86 in the following situation. The net gain is 4 crores in each of the 3 years & net consideration is 7 crores in each of the 3 years. The total cost of the new property is 21 crores.