There are a number of properties that are automatically created for every ItemType. That report in particular doesn't display these system properties if no changes have been made to them. These properties include things like id, config_id, created_by_id, state, etc.
Christopher, thank you for your explanation.
It surprises me because created_on and created_by_id (both system properties) are displayed in ItemType Definition Report for "CAD" but not in ItemType Definition Report for "Part". The number of properties shown is significantly different.
No changes were made to any properties.
The CAD ItemType has been modified to include a label on both the created_on and created_by_id properties. By default, these properties are created without a label. This is why they show up on the definition report of CAD but not Part. You'll notice that many of the other system properties on the CAD ItemType also have labels which would explain the difference in the number of properties in both reports.