I'm sure the artist-side upload function for the products was tested and developed before we ever got the option to sell the things. The supplemental file is uploaded, it's given a file name, thumbnails and display images (picture on bedspread, picture on shower curtain) are generated and named, the page code calls to those files, and then the page is displayed. A glitch has prevented these particular display images from appearing on my page. Maybe they were never generated, maybe they were misnamed. For whatever reason, the call is not being completed and the images aren't displaying.
It's not all that complicated, it just needs a little fixing.