Perhaps if every move was less of an adventure you wouldn't have so many issues. Migrating through new versions of iPhoto, backing up, migrating user acoounts... none of these things create duplicates or have any effect of the date of the photo if done correctly. Sounds like you have been importing libraries instead of moving them.
iPhoto has always used a database, and always used the file system. All your photos are stored in the file system, in folders, untouched in any way. Nothing has chnaged there at all since v1.
There is a way to bulk fix dates in iPhoto, been there since v6 in 2006, if I remember correctly.
Obviously we speak to different pros, but none of the ones I speak to uses a bare file system. All are using apps like Lightroom, Aperture, Portfolio etc, because the volume of images is just too great.
I wonder if you're confusing the file date with the Photo date?
There are two kinds of metadata involved when you consider jpeg or other image file.
One is the file data. This is what the Finder shows. This tells you nothing about the contents of the file, just the File itself.
The problem with File metadata is that it can easily change as the file is moved from place to place or exported, e-mailed, uploaded etc.
Photographs have also got both Exif and IPTC metadata. The date and time that your camera snapped the Photograph is recorded in the Exif metadata. Regardless if what the file date says, this is the actual time recorded by the camera.
Photo applications like iPhoto, Aperture, Lightroom, Picasa, Photoshop etc get their date and time from the Exif metadata.
When you export from iPhoto to the Finder new file is created containing your Photo (and its Exif). The File date is - quite accurately - reported as the date of Export.
However, the Photo Date doesn't change.
The problem is that the Finder doesn't work with Exif.
So, your photos may have the correct date, and so does the file, but they are different things. To sort on the Photo date you'll need to use a photo app.
