Imported Keyword Tags Problem

I think I understand what you are saying.  You have assigned People tags to new files in a new catalog on your new machine.  You have imported old People-tagged files to the new catalog.  These contain duplicate names of People you have tagged.  Do I have this right?

The problem you are facing is that when you import previously tagged files into a new catalog, they are tagged with Keyword tags that are different than People tags.  They will be found in the Imported Keyword Tags category in the tags panel:

If this is the case, there is a fairly easy way to eliminate the duplicate names in the tag hierarchy and put the imported files into the correct People name tag.  Here is what I would do:

1. Select the duplicate name in the Imported category to display all of the imported files for the duplicate name.
2. Select all of the displayed files (Ctrl+A on a Windows machine)
3. Tag the files with the People name tag.  All of the files will now have the correct People tag.
4. Delete the duplicate name from the Imported Keyword tag hierarchy.  You will now have all the files for that person tagged with the correct People tag and will eliminate the duplicate names in the Tags panel.

You can use the same approach with other kinds of keyword tags.