Absence of proof is not proof of absence...agreed. But is absence of evidence not evidence of absence?
Personally i do think that an absence of evidence for something for which evidence is sought is indeed evidence of its absence. Not proof of its absence but evidence.
Example: The absence of concrete evidence of Bigfoot is at this point evidence that it does not exist. It's not proof that Bigfoot doesn't exist but the sheer lack of evidence seems to me itself to be disconfirming evidence.
What are your thoughts?