How does the People Album work when photos are synced across multiple devices

markwmsn wrote: … At one time, every device did its own People recognition processing whether it was linked to iCloud or not. Later, various users deduced that devices seemed to be syncing some People information across iCloud Photos, possibly changing from release to release, but they don't seem to have documented the extent or methods involved. (Somebody please correct me if that's wrong.)

As far as I can tell, that's about right. It looks like information about certain facial features are transferred with synchronization, including the name and where to put it.

I have picture with a person recognized and unnamed, but I entered her name on my computer, and now (less than two minutes later) she is named on all the others. I named someone on another picture, and it changed within seconds on the iPad.

BUT, I have a picture from March on my Mac with 5 people recognized and named, but on my phone and iPad it's 4 recognized and named. And since #5 is unnamed on the iPhone and iPad, then never can be, since #5 is already recognized on the Mac, and so can't be added.

Unrecognized-but-named people on the Mac are, on the iPad, indistinguishable from recognized-named people.

I have a picture on my iPad who is recognized and named, but who is recognized and not named on the Mac!

At one time, every device did its own People recognition processing whether it was linked to iCloud or not. Later, various users deduced that devices seemed to be syncing some People information across iCloud Photos, possibly changing from release to release, but they don't seem to have documented the extent or methods involved. (Somebody please correct me if that's wrong.)