When viewing the properties of an item, there should be an option to view a history of notifications that were triggered for that item. This would allow people, such as an uploader, to verify that the intended collaborators are receiving the information about the upload, and take action if the notifications are not triggered.

Potentially having an item saying something like "notification suppressed" for those who have the options disabled or if the folder settings are defined to disable notifications would be useful as well.