I am not seeing the answer for this problem - I imported 14K photos from my PC to Mac, had them ready and cleaned up, no dups, etc., then after importing, most of the photos do not have the correct date taken, which causes a lot of problem to viewing all my photo. It is taking the date created as the date taken. I cannot seem to change anything else about it. With all pictures I have, I renamed ALL of them to the date taken in the format 2013-0520-xx, just so I would be able to keep up with them in the transfer. So I am able to know the date by the file name stored outside of iPhoto. Then I ran iPhoto for the first time, and everything is a mess without a way to fix it. HELP
The problem is most likely, that your original photos didn't include timestamps. So iPhoto changed the date to the day you imported it. You have to use ExifTool or Lightroom or any tool that can edit EXIF metadata correctly and then import the files again.