> It allows specifying a constraint - that you can't have two rows with the same values even if one of the values is a NULL. That's prohibiting duplicate NULLs. The change allows you to prohibit duplicate NULLs.

Sure.

> Here, "Kim" is car-less (NULL in the CarID field) twice, which makes no sense.

The relation makes no sense to start with, it didn’t need duplicate nulls for that.