Task: Question Understanding
Input (English): Passage: The site of the battle is located near U.S. Highway 56, about three miles  east of Baldwin City, and is partially within Robert Hall Pearson Memorial Park, designated by the state of Kansas in honor of one of Brown and Shore's fighters who gave a handwritten account of the battle. Signs placed throughout the battle site point out where the battle began and ended. Efforts are underway to preserve both the Pearson Memorial Park and the Ivan Boyd Prairie Preserve across the road. In 1970, to commemorate the 100th anniversary of the founding of Baldwin City, Baker University professor and playwright Don Mueller  and Phyllis E. Braun, Business Manager, produced a musical play entitled The Ballad Of Black Jack to tell the story of the events that led up to the battle. The Ballad Of Black Jack played as part of the city's Maple Leaf Festival from 1970-83 and again from 2001-05. It also played in nearby Lawrence in 1986 and in 2006 and 2007 as a part of Lawrence's Civil War On The Western Frontier program. In 2012 the National Park Service designated the battlefield a National Historic Landmark.
Question: When was the last time the Ballad of Black Jack was played as part of the city's Maple Leaf Festival?
Output (English): date