A dec page is sufficient. I think you might be thinking of a binder, Skittles.
For FDIC banks:
(2) Sufficiency of demonstration. For purposes of confirming a borrower's existing flood insurance coverage under paragraph (b) of this section, an FDIC-supervised institution or its servicer shall accept from the borrower an insurance policy declarations page that includes the existing flood insurance policy number and the identity of, and contact information for, the insurance company or agent.
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All opinions are my own, not my employer's