Usually you will get waiver letter from DOS two weeks after you get the waiver agreement from China Consulate. One week later you will get the formal waiver letter from USCIS. That is essential for a J1 visa holder and also for the dependents came from China directly. Looks you failed to send them your normal waiver letter when you submit you i140 application. So, do you best to satify this require. Otherwise I am afraid you will have trouble.