Hi,
it is not about finding the ''many old photos from 20 years ago without metadata'', it is about that very high probability that the corrupted photos are among the ones with missing metadata. That helps you by narrowing down the number of photos you have to search through.
If you verified all the photos and videos, did you check for other type of files like pdf and dng?
On page 6, the MutantSquid has a suggestion for that.
Quoting MutantSquid:
1.
''Look for PDFs and DNGs! While 10.15.1 fixed mine, I had also done the following:
look for broken files; these will show as a light grey square that cannot be opened and, when exported, is a file that preview cannot open (I had 4, 2 pictures from a GoPro and 2 videos)
search for unsupported file types - it appears that iCloud and Photos support PDFs and especially DNGs - they preview and are readable, but the curation process does not like them one bit - after my library curated, I put 2 DNGs back in and the process jumped back to its frozen point and could not curate the DNGs.
the PDFs and DNG issue really threw me. The only way I even knew they were there was by option clicking the Photo library, choosing “show package contents”, then combing through the folders in the “originals” folders (note - DON’T delete directly from the originals folder; if you find a DNG or pdf, search for them IN PHOTOS and then delete that way. ''
2.
''Unfortunately there isn’t one SUPER easy way to find them, but after obsessing over this for a week I found a few things that might help.
Smart Albums! Using Smart Albums helped a lot. I found in my library that the corrupted photos would often be missing metadata. So, I created smart albums to sort for items that had things, like “camera model” and “is empty” or “ISO” and “is empty”.
Check iCloud online. When I would log in and look at my photos on iCloud to it would always state “x photos, x videos, 3 other”. The “other” was driving me mad, since there were no more blank pictures or videos...turns out, it was 3 PDFs.
Force download and export originals. This was a huge help. I had my entires library on a 1tb SSD. I exported all originals to one folder, which made it easy to find: a) file types by sorting in finder, b) corrupted files (small or no preview) , and c) Photos gives an error log for files that it can’t export from the database (but oddly, it can export corrupted photos sometimes). ''
Best of luck !!