I don't know if it is Manila Embassy specific, but we tried this and the IV Unit responded with "K-1 Petition Approval Notices are only extended at the time of the interview by the Consular Officer and not before. If your approval notice is past its date of validity on the day of your interview and the Consular Officer approves your application, they will automatically extend the validity of the approval." OP I would suggest this, no matter when the interview occurs, bring updated Letters of Intent to Marry from both parties to the interview. This is good practice no matter what AND if the approval is nearing to the end of its validity date, according to the FSM, the consular officer can ask for updated letters prior to approving the visa.