My late colleague @Warehouse_Rabbit mentioned this before, and I can now confirm: Submissions initially uploaded for 'Everyone' cannot be edited to a higher level: category checkboxes show the 'unavailable' symbol when hovered over, and can't be selected.
N.B.: Status can be downgraded, and switched back if the user does not navigate off the edit page, but it seems 'E'-rating metadata is loaded in a way that pre-emptively locks out adjustment.
