Date of completion and interest provisions under rera

Hi, I am a practicing CA. I had booked a flat in an under construction project back in 2013, when the project got listed on RERA the developer mentioned Proposed Date of Completion as 31/12/2018. Then he got a Revised Date of completion from the authorities of 31/12/2019 and now an extended date of completion of 31/12/2020. I wish to know how many times and how many years can the date of completion be extended ? and from which date will the developer be liable to pay interest to the unit holders ? Thanks and Regards Priyesh