Soceity Share Certificate

I have bought flat in May 2011 from my elder sister. My sister bought it in 2007 from builder. Till 1 month before, soceity formation was not done by builder. Now builder is taking fast steps to complete soceity process as government official are pressurising him. When I bought flat from my sister, we didn't took NOC from builder, so builder has entered my sister's name in Soceity and shares certificate will be issued on her name only. So my question is 1. "Whether I should talk to builder and pay whatever he is asking and add my name in the soceity" OR 2. "Let the soceity formation get complete and get the share certificate transferred from soceity" I would prefer 2nd option but want to know is legally that possible considering purchase date of flats and soceity formation date. If there is any other suggestion, please share.