How are you looking at these dates? If you want to see the PHOTO metadata, then you probably need to be opening in Preview, and looking in the inspector tool there.
You need to distinguish between the file metadata (information about the file) and the image metadata (information about the image in the file)
If you copy a file the copies creation date will normally be set to the date the file was copied. The image metadata inside the file (which you can view in preview with the inspector window, iptc tab) will show the image capture date.
Summary:
The File metadata is kept in the file system, and represents when that copy of the file is created or modified
The image metadata is kept inside the file, as exif and IPTC data. This won't change when you copy / move the file.
(Depending on your system version, if you export unmodified original from photos, you will usually get a file with the same creation date as the image)
