Whyy is there discussion of what happened in Andover?
When Hale returns in Act IV, Danforth asks him if he has been preaching in Andover. While a seemingly innocent question, Danforth's paranoia and Hale's answers shows the reader how other towns have dealt with their witchcraft scares.
Daforth asks Hale
Mr. Hale, have you preached in Andover this past month
And Hale responds
Thank God they have no need of me in Andover.
Like Salem, Andover had a "witchcraft outbreak." However, unlike Salem, the people of Andover have been able to move past the scheming and finger pointing and repair their town. The town has united against the courts and thrown them out of their town. Danforth, with good reason, worries that such a fate might happen in Salem. Hale returns to Salem as a means of atonement for his previous actions (condemning the people of Salem for witchcraft). He knows now that witchcraft is not present in Salem the same way that the people in Andover now realize witchcraft was not in their town.