Hmmm... I can get it to work for people who DO have sources, but I can't get it to work for people who do NOT. I have tried several different ways.
I suppose you could print a custom report of those with sources to compare to your Individual List, but I didn't think that would be necessary. I can't understand why "Does not exist" doesn't seem to work. Neither does "Matches" [blank]. The logic escapes me. Sorry!