@Chekhov MacGuffin: What you've said about the middle-aged couple is certainly reasonable (as ever). After reading your explanation, I nodded as most of your wall-of-text readers have been doing. Actually I weighed a whathisname's suggestion of Sera being the one who asked Hakase about Haibara for a while, then I dropped it because yours is more likely to happen. In comparision with those young women and father-and-son gang, that husband and wife had more chance to gossip about an unacquainted/absent little girl without being noticed as awkward. It amused me when they refered to Haibara as Hakase's daughter, not grandaughter. (just a random thought). There are at least two paralell annoying yet irresistible mysteries are running here, which I'm not sure if they have crossed, and when. 1-The kidnapping fuss 2-Sera's investigation + Okiya's supervision. Gosho has used Hakase's well-known absent-mindedness to 1-leave a hint 2-make a tangle of the ball of wool.
In any case, I couldn't help thinking about "the start of something new". This is, probably, just an hors-d'oeuvre from Gosho.