The public aspect of the content is orthogonal to the public aspect of the data. E.g. let's say the grade record is encrypted. Anyone party to the key is able t

The public aspect of the content is orthogonal to the public aspect of the data. E.g. let's say the grade record is encrypted. Anyone party to the key is able to verify that the record is (un)tampered, but the wide world cannot read your grade. And that is orthogonal to whether the content is mutable or not. It just means that mutation is deliberate and obvious.