I would want certification of which determination is the correct one and you, the financial institution, are responsible for the accuracy regardless of it being obtained from a 3rd party.
If the property is indeed in the SFHA you have a violation for not providing the notice. You should provide the notice now but keep in mind that doesn't cure the violation. If you are fined for the violation then you may want to look to the vendors warranties in the contract.
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The opinions expressed are mine and they are not to be taken as legal advice.