If you refer to the regulations for the acceptance of a private policy, you will see no mention as to how the policy is rated or any mention of flood zones. As long as the policy meets all other regulatory requirements for the acceptance of a private policy and it is written for the correct property, your buildings would be covered. So, no, there is nothing that would say that specifically.
Plus as you noted, even on an NFIP policy, any requirement to refer to the flood zone on the NFIP policy is going to go away.
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