This page seems to imply that you can tell if your glasses are safe by seeing whether they block out all but the brightest lights (direct sun or perhaps a LED flashlight).

But another page from the AAS seems to say you only get a negative result: if you can see anything other than a very bright light through the glasses, they're unsafe. But that doesn't imply the inverse, that if you can't, they're safe, because of UV protection. https://eclipse.aas.org/eye-safety/iso-certification

Can anyone confirm if I've understood that correctly?