caption missing but in iptc in photoshop

Working with 65 images from a photographer covering a wide swath of his long career. Some of the images from one source, but not all of them, have missing file info that is there if I check the file in Photoshop. Specifically the Caption (Aperture) or Description (PS) field. There is text in the Description field in PS, but the caption is blank in Aperture or showing info from another field.

Poking around online I found the IPTC site and it left me thinking that the IPTC format might have changed from an older version to a newer one and the jumbled images might have been captioned in the older format and never updated. Or is there another explanation?

Garrett