Delay in Apartment Registration after Occupancy certificate

Hi Sirs, I bought an apartment with a renowned group in Bangalore in April 2018.The sales team committed to complete it all by Sep,2018..The got OC and offered me posession by Aug ,however I enquired about registration..they keep mentioning government guidelines not yet available..I have paid over 95 percent of amount..they keep mentioning to come and take possession while I am outside india.property is registered under Rera..is it legal to take possession without registration..does completion mean only hand over and possession and we can wait for registration while paying the wholesome amount? Regards, AKJ