I have a folder of wedding photos in my main LR catalog that i needed to edit while away from the studio. I exported the photos as a LR catalog with smart previews and opened this new catalog on my laptop, set rejected flags on reject images etc . Now when I have my studio desktop machine with the main LR catalog and "import from catalog" I get a dialog saying"There is nothing to import in the catalog you have selected" I see none of my rejection flags that were placed on the exported catalog.
LR CC mac os 10.93
This would suggest that the assets are in fact in both catalogs and are equal.
Lets make them unequal:
Go to your Laptop Catalog and select all the images and apply something to them like a star rating or color label (preferably one that you are not currently using. Something that can easily be changed later.
Then close the catalog and try the import again from the desktop. This time you should see a window listing the folders and previews of the images. At the bottom left select "Replace : Metadata and develop settings only" Click the check all button and import.
Now remove whatever the setting was you applied in the Laptop Catalog to force this change.