What documentation should I keep to defend FCC and ISED compliance during audits or customer reviews?

You should maintain a defensible technical compliance file for the finished product, not just the module grant. This should include the FCC and ISED certificates for the radio module; the integration guidance from the module grantee; RF exposure assessments for the final product configuration; host-level emissions verification results, where applicable; antenna specifications and placement documentation; and user manual and labeling compliance statements. Regulators and customers do not accept “the module is certified” as a sufficient compliance argument. They expect evidence that the final product, as shipped, still conforms to the regulatory assumptions behind the original approvals.