Michael John Neill at rootdig.com:
with the advent of searchable databases, most genealogists are not coming anywhere close to tracking what they search for in a specific database or on a given website. ...Read the whole thing. Remember, the dog that didn't bark in the night-time was evidence in Sherlock Holmes' day, and it still is.
I've seen articles where it has been said someone cannot be found in a census. I rarely see where the specific unsuccessful searches are listed out in an attempt to defend the "can't find them statement."