You need to apply to rera in prescribed format about the same. As the requirement of tea registration was also project in which oc was not received on date of application of rera

Project is complete before RERA come into force, no application of RERA. Are you sure 1999 ?

Further no registration required where the area of land proposed to be developed does not exceed five hundred square meters or the number of apartments proposed to be developed does not exceed eight.

And if CC is issued befoer RERA enacted than also dose not require registration.

Once registered then even if subsequently OC is obtained by builder, rera will continue to apply

Only exception by which a builder is not required to register with Rera are plot size and number of flats below the threshold limit specified in Rera

Yes you can come out of RERA if you don't want to sell other units of your project.

withdraw procedures are applicable only for those cases wherein the Authority has not generated the Registration Number/ Certificate etc. 

Yes, you can put oc application in the RERA.

You have to apply before rera authority to cancel the RERA registration for the project as it is already completed in 1999.

Since you have already applied for registration with RERA, which was not required for the construction completed in the year 1999, you may have to follow the further procedures/formalities in this regard to make an exit from the RERA. 

You can call on their office in person and get the details clarified for compliance.