From my experience, it is often common place for developers to promote and sell developments without the building licence in place. However that is not to say that all do. As your lawyer has advised, without this document, you cannot complete nor “turn” the property prior to completion which by the sound of it was always your intention.
Upon the receipt of a building licence a private purchase contract can be issued which will then enable you to assign the contract prior to completion.
I would be interested to learn whether you signed a reservation contract and and what deposit.