Typically you get a statement like “our suppliers have FSC certification.” The implication is you are going to get FSC certified timber.
However, it may well be that the supplier has FSC certification for a different timber entirely such Oak. It sounds great, but is no guarantee that your birch plywood has not come from a source like Russia or Belarus. The Russians make excellent quality birch plywood and its dirt cheap.
Laminate and Ply hold FSC certification themselves. This means they claim on your invoice under their certification that your timber can be traced back to a certified legal well managed forest. They are subject to external audits to verify their claims.
To be sure you are getting sustainable timber use suppliers who hold FSC certification not the ones who talk about someone they know having it.