Think for a moment about the reasoning behind entering sources for your
'facts'. It isn't for sake of completeness or convenience - its so the
validity of the information can be judged.
Especially when you find a new sources that doesn't agree with what data
you already have, you'll probably want to check the old sources and verify
that the information was entered correctly.
Sources are also great to figure out why you know what you know. I've
forgotten why I've linked two individuals together before, and had to review
sources to figure out why I was sure of their relationship.