While performing a search in the organizer I noticed that some of the results carried the yellow missing media indicator. Since all of my images are on a single online drive (C:), I was worried that the images were somehow lost. It turned out that all were from the same directory and that the images were still in tact. However, the filenames had been renamed, probably an error on my part, and that or something else may have caused the catalog to not update.
It occurred to me that if this happened in this contact sheet, it might have in others. I see that there is a Select Missing command, but it appears to only function within a single contact sheet. Is there a way to search the entire catalog for missing media?