In the "Azusa Imposter" arc, how can the people of Nascute not recognize the true Witch of the Highlands? Nascute is an hour's walk away from Flatta, its the closest settlement to Azusa's hometown. Although some events from the Light Novels didn't get into the Manga or Anime, there have been many times Azusa and family have been in Nascute. They went from one end of Nascute to the other introducing Rosalie and showing that she is a friendly ghost after the events of that story arc. In the manga and the books, Flatorte and Laika (as well as the rest of the Family including Azusa) spend a long time in Nascute selling their cookies. Perhaps one or two people who live out in the countryside might not have seen these many events but certainly the other townsfolk would gossip and talk about what they've seen would be able to point out Azusa, The Witch of the Highlands!
They didn't find her at Nascute. That was a town about 60 miles north (about 3~4 days by foot) from a town west of Flatta.
