Bitten by the Windows Explorer Search Bug (err, "Feature") again.
I should have known.
I was at an important client meeting yesterday, and we got into a discussion over what was there and not there in a two sets of text files. The first set was given to me perhaps a couple of months ago, and contained way more data than I needed, as well as duplicates. The other set of files was given to me within the last couple of weeks. I was insistant that certain names and numbers that were present in the first set of files were not in the second set, based upon my use of Windows Explorer search. Of course, there was only one problem: Explorer was not really searching the second set of files, since they were given to me with a .DAT extension rather than the .TXT extension that the first set had been. Explorer does not search files with an extension that is not registered. Here you can fix this "feature". I looked rather silly, I fear, when I had to sheepishly admit I had been bitten by this (again).
This default behavior should be fixed. At least a message should be prominently displayed when you ask Windows to search for *.dat files for a given bit of text, and Windows knows that it will not search those files.
Yes, at some level I know about this, and have patched other installs of Windows to search correctly, but this machine had been recently repaved, and I simply did not think about the different extension on the second set of files.