I've been using this quite a bit lately... yes, I know it's cygwin... but. Anyways
grep -ri "pkAPI [API_NAME_HERE]_" . | sed s/.*pkAPI//|sort
This little script snippet finds me all the functions that exist in the current folder and trims them up with sed before sorting. I just compare the results with my reference sections and 'zing!' I can determine which APIs I haven't documented.