Collections with ornaments in them can be renamed (changes all matching records) but cannot be deleted while in use. Empty collections can be deleted.

Untick anything you don't record. It disappears from the Add/Edit form, the detail view and the completeness score. Nothing is deleted - tick it back on and your values are still there. Name and Collection are always kept.

Items in use can be renamed (updates all matching records) but cannot be deleted. Custom entries that aren't in use yet can be removed from the dropdown.

Scanned reference catalogs. Tap one to read it - ornaments whose Info Source mentions a catalog page link to it automatically.