Identify smart albums

One supposedly smart album doesn't have all photos as I entered - or thought.

I am not sure, what you are asking about. You cannot enter photos into a smart album. Are you asking about photos, that should have appeared in a smart album and do not appear in this album, according to the constraints of the album?

Which album are you referring to? Ad which photos are missing from the smart album?

You can only control smart albums you create yourself. All predefined albums, created automatically by Photos, are following fixed rules, but you cannot modify the rules.

If a smart album, created by yourself, is not containing all items you would expect in the albums, check the properties of the missing items.

Yes, that is how it is supposed to happen. You do not even need to first elect any photos to create a smart album. The photos inside a smart album are only determined by the rules.

• Create the smart album from the File menu: File > New Smart album, then define the rules.
• Or hover the pointer to the right of "My Albums", until the (+) button appears, click it. Then select "Smart album" from the menu.

You can think of smart albums as being computed albums, that will always update themselves automatically, based on all photos or videos in our Photos Library.

• The standard albums are like enumerated sets of photos, created by adding photos to them. We can create them by selecting photos and dragging the photos to the sidebar to add an album with the selection, or by creating a new, empty album and dragging photos into the album.

Control click on the album in the sidebar in Photos. If it is a Smart Album, one of the options will be "Edit Smart Album."