It seems to show most of them (although I haven’t cross referenced the two lists).
It’s because he only wrote a single story in the past few hundred stories. You can still train +/- on him, you just need to find the story and train on that story. (Right-click the story title in either the Feed pane or the story titles pane to see the trainer. In the social branch I’m working on now, this will be easier. Alternatively, you can also click his name in the Feed view.)