What I didn't know when I first posted this was that each "???" is replaced by the duty name once you unlock the corresponding duty. And they subsequently disappear from the list as you complete them. As someone else said, apparently the "???" is to prevent any spoilers that might be caused by the duty names. (I remember how the track names in the soundtrack for Star Wars: The Phantom Menace, which came out before the movie did, spoiled the fact that Qui-Gon Jinn died. So you never know what can spoil a major plot point.)

Thank you for all the excellent responses. I was pretty frustrated when I first saw this, and you were all quite helpful.