Conveyance of 97 flats out of 100 flats is done

Hello experts, I am looking to buy out a flat in a society. This society has 100 flats out of which 97 are sold out. There are 3 flats which are unsold and remaining with the builder. I am looking to buy one of the three unsold flat. While going through the documents, it is known to us that society is conveyanced, l however, only 97 flats are conveyances and 3 flats which are unsold yet are not conveyance My question is, how can the flat I am looking to buy can be conveyanced?