Wait wait wait… immutable means unchangeable! In your analogy this would mean if someone changes anything about them, like a name due to marriage or gender due to affirming care, they become a new object. And you can, but shouldn’t assign that new object the same UUID.
I would just argue that objects of the Person-type are mutable, because basically everything about them can change without modifying who they are. The only thing immutable about a person is any one Moment-type object in their past.
Edit: I found your comment to be an interesting take on the concept, thank you!