Unreported is usually used in contexts implying neglect or oversight, which can be negative. The charity aims to help the unreported victims of the conflict.
Pro Tip 2/3
Invisibility
'Unreported' suggests a lack of visibility or attention to something that might be significant. Unreported environmental violations can have serious consequences.
Pro Tip 3/3
Data Implications
Using 'unreported' hints that available data or information is incomplete or misleading. Health officials are concerned about the high number of unreported cases.