System vs user data
User data is authored by the issuer and defines the disclosure's meaning.
System data is computed at issuance, such as identifiers, timestamps, and hashes. It does not change the disclosure's content.
Draft data is editable. Issued data is fixed and immutable.
Why the distinction matters
The document is easier to interpret when the reader can tell which parts came from the issuer and which parts were added by the system to stabilize the record.
How to read the two kinds of data
User data expresses what is being declared. System data expresses when and how the declaration became an issued record.