You are considered to have relinquished your U.S. citizenship on the earliest of the following dates:
The date you renounced your U.S. citizenship before a diplomatic or consular officer of the United States (provided that the voluntary renouncement was later confirmed by issuing a Certificate of Loss of Nationality).
The date you furnished the State Department with a signed statement of your voluntary relinquishment of U.S. nationality confirms the performance of an expatriating act (provided that the voluntary relinquishment was later confirmed by issuing a Certificate of Loss of Nationality).
The State Department issued a Certificate of Loss of Nationality on the date.
The date a U.S. court canceled your Certificate of Naturalization.
Suppose the earliest of these four events is when you renounced your U.S. citizenship before a diplomatic or consular officer of the United States and were issued a Certificate of Loss of Nationality. In that case, you can file your final return and Form 8854 now and indicate the date you renounced at the embassy as the date of expatriation, even if you are still waiting for your Certificate of Loss of Nationality to arrive.