Based on your comments, I assume the borrower didn’t notify you of the address change. (Depending on the circumstances of the loan, this could be out of the ordinary meaning your loan department might need to look into the loan/borrower). Either way, I’m sure your bank has already made contact with the borrower to determine his/her current mailing address.
As it related to the disclosures, it is the borrower’s responsibility to provide you, as the lender, with a change of mailing address so you may communicate timely and effectively. The flood regulations require that you notify the borrower of inadequate coverage and the need for the borrower to purchase flood insurance. It seems you did attempt to notify the borrower as required, but because the borrower failed to notify you of an address change notification was halted – the fault that it wasn’t received lies with the borrower not you as the lender. If you have documented the circumstances and your efforts to deliver the notice I don’t believe you would be criticized for following normal force-placement procedures. I would recommend that you make every attempt to provide the notice to the borrower ASAP, and remember to document your efforts. You want to create a clear picture for auditors and examiners.