For now, I searched for *(1).mp3 files and deleted them, ran Auto Import with Fix Broken Links = Yes.
Not ideal, but it works.
Caution: MC will name files with (1) after the name even if the files are not really there, if MC
thinks the files are there (i.e. - they are still in the library database) such as they were deleted from the drive in Windows Explorer rather than inside MC. This results the files named with (1) being the
only ones, thus deleting them will cause their loss.
I find it best to run the import (with "fix broken links" checked) before addressing the files with (1) in the name.
In many cases this gets the 'phantom files' (mentioned above) removed from the DB and allowing the files to be renamed-from-properties with MC removing the (1) for you. If MC still adds the (1) then it is likely there is still another 'copy' in the Library DB.