You may want to send feedback to Apple and request a refined smart album.
The feedback form is here: http://www.apple.com/feedback/photos.html
The more people request improvements, the more likely it will be that Apple will be doing something about it.
I am glad, this smart album is back at all. In earlier versions of Photos we did not even have this album.
Apple removed the long list of unnamed faces completely from Photos, when Photos 3 on High Sierra came out and finally the faces could be synced with iCloud across all our devices. . The previous versions of Photo still had a pane of unnamed faces, showing only unnamed faces. In Photos 1 and Photos 2 we could delete the unnamed faces of strangers and keep only the faces that we want to name.
The command to delete faces has been removed in Photos 3, and as a consequence, we also have no longer a list of unnamed faces at all, because we can no longer weed it out reject the faces of strangers or Artefacts. The list of unnamed faces is now ion the current version of Photos pretty useless, because the faces we would want to name will be hidden among the thousands of unnamed faces of people we do not even know. It is now like looking for a needle in a hay stack. We can only speculate why Apple does no longer allow us to dismiss faces of strangers or artefacts, that are no face at all. my guess is that the scene recognition in Photos needs to keep all detected faces to be able to recognise crowds or some types of events.
As we are now stuck with all unnamed faces and cannot do much about it, I am only naming unnamed faces when I import new photos and browse them to delete the bad or boring shots. When I come across an unnamed face of a person, that I want to have named on a photo I like to keep, I name it, but I no longer search systematically for all unnamed faces. For the people, where many photos have been named, It is easy to find new unnamed faces by opening the album of the person and using the command "Confirm additional faces". This dialog is showing especially all additional faces that Photos recognised as the sam person. We should get these faces out of the way before searching for more unnamed faces and adding faces manually.
