Adding to what markwmsn said, the Recents view always shows all of the pictures in your Photos Library in the order of the date they were added. This can't be changed. This album always provides the same view so that, when something goes wrong or seems off, you (and we) can depend on it showing the same thing, and there's no chance that someone snuck in and changed the order or removed pictures. On the other hand, the Library view shows all of the pictures in your Photos Library in the order that their metadata indicates that they were taken.
To confuse issues, when a batch of pictures is added to the Photos Library, they don't arrive in the order they appeared at the origin. They shoot through multiple cores and arrive more or less randomly. So all the pictures in a batch will appear together in Recents, but they may not be in any recognizable order. As markwmsn said, they will be in date order in the Library view.
Most of us don't use Recents or Library to view our pictures-- we make albums of our own so that we can find what we want--so we may transfer all the Grand Canyon pictures to a Grand Canyon album. And, since Albums are just a list of pictures to be viewed together, an image can be in multiple albums without taking up any extra space. The picture of "Aunt Ethel at the Grand Canyon" can be in the "Aunt Ethel" album with other pictures of Aunt Ethel, and it can also be in the "Grand Canyon" album with pictures of other people at the Grand Canyon. And it can also be in the May 2018 album. This is very powerful in organizing pictures.
I hope this helps make sense...
