I think I finally have the answer. I have imported the same files into Photoshop Elements 2012 and 2020. My captions (entered at TAG 010E) are transferred into the Catalog in 2012 but not 2020.
Photoshop Elements 2012 imported the captions from the EXIF II locations (i.e. TAG 010E), but Photoshop Elements 2020 does not. Instead it imports them and saves them to a XMP location. That means I have to learn to read and write to those locations in order to accomodate the 2020 version.
When I add a caption to a picture in Photoshop 2020 Organizer and Save Metadata it places the new caption in the XMP region, leaving my caption at TAG 010E. It displays the new caption with the figure, but no longer reports my caption as Image Description.
The bottom line: Since the Adobe programmers removed the option of importing the caption from the EXIF II metadata after the 2012 version, I need to learn how to rewrite the XMP data to include my captions.
Thank you very much for helping me finally understand the problem and seeing a possible solution. Time will tell whether at my age (91) I can still learn the XMP format (find what points to what) and modify my .JPG header editing program.