If you have a customer relationship, then they can sign in (and accept your ToS) - and then you can, if they allow, track them that way. Similarly for re-activa

If you have a customer relationship, then they can sign in (and accept your ToS) - and then you can, if they allow, track them that way. Similarly for re-activation campaigns, one can use something like UTM. Don't need to track everyone on the internet with generic stats mechanisms (like Plausible provides) for that.