This is mostly just OCD, as I spent all this time taking snapshots of my sims so they could order a photo album. I moved them around, and now all of the snapshots I had taken are filed under the Other tab. They're no longer personal to this family, and cannot be selected with the Order Photos action. They're all filed in the storytelling folder, but is there a way to assign them back to a particular household?

Find a snapshot which is listed as belonging to the household, and copy the first part of its name (before the underscore). Rename the old snapshots and thumbnails to use the same first bit of name.