I have noticed that. Looking at the existing episode summaries we have for the first episodes, we have the episode about Ladonna, one for Francine, one for Muffy, 2 for D.W. and Emily together, one about Mr. Ratburn, one about Mei-Lin, and two about the Tibbles.

Now we can only speculate with the names we have for the rest of the season, but I doubt "The Last Tough Customer" will be about Arthur, "Brain's Chess Mess" and "Brain's Biggest Blunder" are obviously about Brain, "Buster's Book Battle" and "On the Buster Scale" are obviously about Buster, and "Fern and the Case of the Stolen Story" and "Sue Ellen Vegges Out" are obviously each about the character in the title.

That leaves us with three episodes that could even possibly be about Arthur: "Baseball Blues," "So Funny I Forgot to Laugh," and "The Best Day Ever"