Facial recognition not working

I have lots of people pictures in a large folder. LR Classic recognizes about 1/4 of them and gives them the right names, but on most of them it just gives a questsion mark, even though many of the pictdures are identiacl or nearly identical to those in the "Confirmed" section. I've tried using "Similar" under People>Find Similar Faces, it will only show that very picture in the lower window, even though there are many faces (like at least 30-40) that are the same person and almost exactly the same view of their face.

How can I get facial recognition to go out and get the other faces that are similar? I'm using a 4 TB SSD on my Mac but the pix are on my external drive which is a spinning hard drive. I've left the computer on overnight and it doesn't go to sleep, still no updates.