31 CFR 850.403: Notification of post-transaction knowledge.

A U.S. person that acquires actual knowledge after the completion date of a transaction of a fact or circumstance such that the transaction would have been a covered transaction if such knowledge had been possessed by the relevant U.S. person at the time of the transaction shall promptly, and in no event later than 30 calendar days following the acquisition of such knowledge, submit a notification pursuant to § 850.404. This requirement applies regardless of whether the transaction would have been a notifiable transaction or a prohibited transaction.

Note 1 to § 850.403:

A U.S. person's submission of a notification pursuant to this section shall not preclude a finding by the Department of the Treasury that as a factual matter the U.S. person had relevant knowledge of the transaction's status at the time of the transaction.