If you share your lists with someone, you may notice that sometimes there appears a blue dot in the upper right corner of the lists icon:
It means that as a result of the last synchronisation the content of the other lists (not the one you're currently viewing) has got changed.
Plus in the list of lists there appears a blue dot next the titles of the lists, that contain the changes:
If you open such a list, you will see the blue dots next to the names of the changed/added products:
This feature lets you avoid missing a new list of products and the updates in your lists.
The text that says "Your data is up-to-date" means that the synchronisation has been successful. Or, if the last synchronisation has failed for some reason, you will see the time and date of the last successful synchronisation.