A close look at the suggestions have found this feature has been requested by others as well:
Duplicate check between databases, for references of a search result or group, for single references
https://community.endnote.com/t5/EndNote-Product-Suggestions/Duplicate-check-between-databases-for-references-of-a-search/m-p/153154/highlight/true#M12592
Basically, EndNote lacks an very important feature of “Reference Manager 12”, which I used for many years.
Again, becasue EndNote thinks “Smith, H.K.” and “Smith, H. K.” (a space between H. and K.) are different, if you try to “Find Reference Updates”, it will show “All are up to date” for “Smith, H.K.” although there is an update with “Smith, H. K.” (a space between H. and K.).