LetsGoThor wrote: At iOS 18, how do you know when Apple has finished finding all the people it can?
Unfortunately, there's no bell that rings when Photos finishes a scan. It tries not not interfere with your work, and it tries not to exhaust the battery, so the best way to encourage scanning is to plug it in, provide it good internet access, and leave it alone for a while.
is there a way to tell the tagging that there are people it missed?
No-- it either sees a face or it doesn't. Re-scanning will occur with OS updates, but otherwise, once a scan has occurred, doing the same thing again would just give the same results. It's a machine, after all.
Face scanning is cool, but most of us don't depend on it. We additionally include names in the Caption section, and we can put names there for faces that Photos hasn't found. Captions can export in the metadata with picture files, but face IDs don't. Captions survive OS updates, while face IDs may not.
On a Mac, by the way, we can identify faces that Photos does not. We still use captions and keywords for people's names there, anyway-- they're just more robust than face IDs.