[brisance]

> Furthermore, Person 2 is a hidden node from Person 4, as Person 2 is not within Person 4’s set of immediate notification contacts.

This is the system working as designed. What purpose would be served that Person 4 needs to know Person 2 was also a contact of Person 1? It's not a perfect system, but this is a strawman argument.

The Google/Apple system isn't perfect, and relies on people behaving like responsible adults. The real world isn't like that, as the Corrupted Blood bug shows.