To be fair, it's unintentional radiator testing that's required, rather than everything the module had to go through as an intentional radiator. So, it is a "free pass" for nearly all of it, and a much cheaper one, since you don't have to use a costly FCC accredited lab.
It is completely left up to you how you are going to demonstrate this if they ever come asking for the paperwork proving this. This can be a certification by an independent testing lab, documentation from in-house tests, or perhaps even documentation proving that it is compliant by design.