Since you are so early in the process, I would probably opt for re-doing the restoration rather than trying to "fix" the duplicates. Just to avoid any potential side effects.
I found this "list of common questions" about backing up and restoring name tags here:
How to Back up Name Tags and copy to an another compter
Thanks for trying out Picasa 3.5 and
thank you for your posts! We've put
together this list of common questions
on the topics you've addressed that we
hope will be helpful to you.
Q: Is face tag data stored in the
A: We currently do not store face tag
data directly inside the photo but
this is functionality that we hope to
have in the future.
Q: Since my face tag data is not
stored in the photo itself, where is
my face tags data stored?
A: Face tag data is stored in the
Picasa database and also in the
.picasa.ini file in the folder where
your tagged photo sits. To see the
location of the photo on your hard
drive and the .ini file where the
information is stored, right click the
photo and select "Locate on Disk".
Q: How do I transfer my face tags from
one computer to another?
A: There are a few different ways to
transfer your face tags:
1) You can perform a Backup of your
photos and restore them on your new
computer. This process will preserve
your face tags. ("Tools" > "Backup
Pictures") 2) You can copy your files
and the .picasa.ini file from your hard drive to the new destination 3)
Upload your face tag albums to Picasa
Web Albums and download the album to
the new destination