How Do I Know Which Photos Have No Date?
Spotting the undated photos in a big library, and what to do about the ones that cannot be recovered.
Sort the folder by Date Taken. Everything that lands at the bottom with a blank date, or clumped on one impossible day, has no date inside it. On a Mac, add the Date Created column in Finder's list view and look for the same pattern.
Photos from a Takeout export almost always fall into this group. So do screenshots, downloads, and anything that has passed through a messaging app. The camera never wrote a date, or something stripped it later.
Takeout JSON Metadata Fixer reports exactly how many photos it found a date for and how many it could not, before and after the run. The ones it cannot fix are the ones where no date exists anywhere. Free for 500 photos.