There you go!
Just import the remainder of the photos in all of your image folders.
One thing: Lr supports only these file formats: Raw-images, DNGs, JPGs, PSDs, TIFFs. Any other file format will not be imported. So if you have images in any other file format you'll be able to see the files in Mac Finder / Win Explorer but not in Lr. Then you will have a different image count in Lr than in Mac Finder / Win Explorer.
Also, Lr counts Virtual Copies (VC) as images; but you cannot see a VC in Mac Finder / Win Explorer since a VC exists only as a data set in the Lr catalog, and not as an image file.
So this is another cause for different image counts in Lr and in Mac Finder / Win Explorer.