Any device you've told to ignore permanently, is put into the Unknown Devices screen in the web admin.
In the case of IP devices, they are keyed by IP address and MAC address
In the case of other devices such as internal disks, or PCI or USB devices, whatever is returned from the Plug and Play plugin is displayed here. If it was matched to a device template, a device template # is also shown. You will have to look a bit to match your devices...
Once you've matched your device, simply press Unlock, and it will be added back into the PnP queue for later detection. You can quick reload router to force this action.
I hope this helps,