Cross testing exploit with vulnerability scan results

Hi Fellow testers,

I've been conducting pen tests since 4 yrs now... the methodology I
follow is that we exploit or attempt to exploit ONLY those
vulnerabilities that a vulnerability scanner identifies. What if the
appropriate check or signature in the vulnerability scanner was not up
to date or had some coding issue or was not comprehensiveness enough
(or anything else) to identify a real existing vulnerability on a
system. This can result in serious false negatives. Would downloading,
installing and cross testing all available exploits for an identified
service be a good idea to minimize such a case? How many people have
faced such an issue or a similar issue? For me I faced this issue with
some  bug in Nessus recently.

This is something like my NMAP says there is IIS6.0 running on port
443 of a target server. I do a Nessus scan on it and it doesn't report
anything. I then download all available exploits for IIS6.0 (or for
all version of IIS? would this make sense) from securityfocus.com or
securiteam.com or similar source and run it manually on the target
system.

Eagerly await opinions.

THNX

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