Photo creation date changed on last sync

Any thoughts on how to capture the correct date, without the need to manually alter each video metadata?

That is what I am doing.

I am using my script to lift and stamp the metadata from one one phot to other selected photos and videos: Script: Lift and Stamp all Metadata from one Photo to Other Photos

I'm using iMovie mainly to stabilize my video clips, that I have taken with a handheld camera. And so I have to adjust the date in Photos after rendering a new video in iMovie.

Now that the sync is done, I noticed the file creation date on some, but not all photos on the Macbook have yesterday's date rather than the date the photo was created. I had to speak with another senior tech today and he told me that was normal behavior and there was nothing that could be done. How is that even possible? If it was normal behavior all the photos would have yesterday's date, not just some of them

As far as I can tell, it is the syncing with iCloud that will change the file creation date for some photos. Are you using the option "Optimize Storage" with iCloud Photo Library? In that case not all original image files will be stored locally in the Masters folder. They will only be downloaded to the Mac, if you are using that particular photos for sharing or editing.

And the download from iCloud may have a different file creation date than previously. If you are syncing several devices with iCloud and there are duplicate images, iCloud Photo Library will recognize the duplicate and store only one version of the file. If the file had different creation dates on the two devices, the date will change on one of the devices - one creation date will be lost by the duplicate removal. But the embedded EXIF capture date will remain the same, and that is what really matters.

For the same reason, synced photos will not always remain in the same subfolders in the Masters folder.

To access your original master files, it is safer to use "File > export" to write copies of the master files to folders outside the library.

Either you are looking at a different library, not the one that Phots is currently using, or you enabled "Optimize Storage" in the "Photos > Preferences > iCloud". Are you using "Optimize Storage"? Then the photos in the Masters folder will come and go, because the main storage of your Photos Library will be in iCloud.

If I change me settings so that we are not optimizing storage then I may not have sufficient space on my internal hard drive to download all the originals. Is there a way to do this incrementally so I can then move the originals to an external drive, or is there a way to have them download directly to an external drive?

Photos on El Capitan does not have the option to select an album and request, that all photos from this album will download to the library. On El Capitan you have to click each photo to view it enlarged to force the download, or use "File > Export".

To download directly to the external drive, you could create a new, empty Photos Library and make it your system photo library, then enable it for iCloud. Disable "Optimize Storage", then wait for all photos to download to the library on your external drive.