Duplication/Corruption of Music files
Looks like turning off "Connect with Xbox Music"

seems to have resolved the duplication and corruption problem with music files. I have a handful of unknown items - will have to check the mp3/WMA tags to see if there is a valid explanation for this, but so far...most look good. Did my transfer via Windows Explorer directly to the SD card. Kept getting a host of "could not synch" errors when I used the Windows 8/Desktop synch apps.
We will see...
Update...I checked all my MP3/WMA tags in mp3tag desktop app and found a few discrepancies - album names were inconsistent, so were some artist names. Changed all to make sure that the common values for all fields were the same for each album, then connected my phone via USB to my PC, and copied and pasted the changed albums to the phone. Checked again, no more problems. I have one entry for each album, and no duplicate songs. Also no negative space in the Other category in Phone Storage.
Key seems to be to make sure that the Music +Videos setting for "Connect with Xbox" is not turned on to make sure that Xbox does not attempt to overwrite my tag entries.
Not sure why I cannot synch using the Desktop/Windows 8 apps. For my purposes, Windows Explorer does the job better, anyway. Why mess with success?