In another comment, I said

I’m not logging them. Though I guess it’s possible someone could create a mostly private post and @ a user to have it show up in their inbox. The point being that some communities do not have many users, so the list of users will not be very long. There definitely are groups who have been granted much larger dragnets than the sizes of many communities here.

Though, I agree, I think they’ll just have a list of IPs unless they’re using a browser that still supports third party cookies (and have other previous tracking information)