Correct.
Senior signed the certified mail return receipt notifying him of the impending but not yet held court hearing on his wife's motion for divorce.
There is no evidence, IIRC, of Senior having received a copy of the final filed court order of divorce after the March 5, 1964 hearing, which Senior declined to attend or contest.
Senior was “busy” at the time (jumping co-eds) and defending his immigration status and may not have informed INS of the exact date of the divorce as it would weaken his immigration status not to have a US citizen wife and kid, which he discovered too, late, it appears.