[oston]

Thanks for all these helpful posts. They prompted me to look at metadata more deeply.
I first saw the alt-text entries for this set of 53 images while looking at the metadata in Bridge. But when I looked at the images in Photoshop, the entries that were in alt-text (Accessibility) in Bridge were in Extended Description in Photoshop.

CORRECTION.
Photoshop DOES display the same alt-text metadata as Bridge and Photomechanic. There was an entry error in the two files I happened to be looking at in Photoshop. The alt-text had been entered into the wrong field.

But in PhotoMechanic, a widely used program for managing image metadata, the alt-text entry agrees with the Bridge format. PhotoMechanic gives me a lot of control over the metadata of the images. It's over 10 years since I used PM, so I'm very rusty. But if more metadata variations are needed, things might come back fairly quickly.