Album Sales Handwritten, 466,000;  Illuminate,  376,000;  Shawn Mendes, 281,000;  The Shawn Mendes EP, 105,000;  MTV Unplugged, 8,000;  Live at Madison Square Garden, 8,000;   Top-Selling Songs "Stitches," 2.7 million; "Treat You Better," 1.1 million; "There's Nothing Holdin' Me Back," 1.1 million; "Mercy," 1.1 million; "I Know What You Did Last Summer" (with Camila Cabello), 807,000; "Life of the Party," 750,000; "Something B