I agree that it was in one of the FDA Q&A's. Likely one of the broken/circular link ones they have all over their FSMA pages.
They're in edition 7 of this guidance which no longer has the specific language, just the below guidance:
M.2 Is a registered facility responsible for ensuring that the companies with which they deal are registered?
There are no direct penalties for doing business with a company that is not registered. However, if a company offers food for import into the United States and the food is from a foreign manufacturing facility that is not registered, the company may be unable to complete the prior notice for the shipment (21 CFR 1.281(a)(6)), which is required to import the shipment.
M.3 Is a facility required to provide its food facility registration number, assigned by FDA when the registration is submitted, to customers or other businesses who request the number?
Is a facility prohibited from revealing its registration number? Section 415(a)(5) of the FD&C Act provides that certain registration-related information, including the registration number, is not subject to disclosure under FOIA. However, this does not prevent a facility itself from disclosing such information. In fact, for imports, a facility will Contains Nonbinding Recommendations Draft– Not for Implementation 59 likely need to provide its registration number to any downstream commercial entity who will be submitting prior notice for a food manufactured by the facility (see 21 CFR part 1, subpart I). The FD&C Act does not prevent a foreign facility from entering into an agreement with its customers to limit the circumstances in which the facility’s registration number may be disclosed to third parties.
M.4 FDA’s list of facilities and registration documents are not subject to public disclosure. How do we know that a supplier, for instance, is registered?
Section 415(a)(5) of the FD&C Act provides that certain food facility registration information is not subject to disclosure under FOIA. However, disclosure of such information by the facility itself is not prohibited. FDA expects that generally, foreign suppliers and their customers will resolve this question as part of their agreement to buy and sell food for consumption in the United States.