Turns out it was something very minor, but difficult to identify in my case...
Since the X5 BT system won't recognize whether contacts are home/work/mobile, etc, I modified all entries in my 'Mobile Contact List' in Outlook to indicate what type of number they were. I did so by adding "-m" for mobile, "-w" for work, or "-h" for home.
e.g.
Smith, Bob -m
Smith, Bob -h
Jones, Sara -w
After that, only about 10 of my contacts transferred
As it turns out, most of my contacts have multiple numbers, so there were only a handful that did not have a dash in the name... well, after staring at the screen for a few minutes, I realized that it was only
these same contacts that transferred properly -
NONE with a dash transferred at all!!
So that was it... if there was a dash in the name the BMW BT system didn't recognize it, and omitted it from the transfer (every other character seems to work fine). So I just removed the dash from all of the contacts, resynced, and
VOILA, problem solved
