Imported photos don't show up in Photos Library
Just noticed that photos that I've imported into Photos don't show up in the Photos Library, only under Imports.
In an earlier discussion of this topic it was recommended to go to Image > Adjust Time and Date and set the time and date to the correct time and date. What does "correct time and date" even mean here. All my imports have the time and date of the import as the time and date. For none of them do I have any idea what the "correct" time and date is. And what has this got to do with whether photos appear in the Photos Library?
Thanks
MacBook Air 11", macOS 10.14