Matt Poitras has been the story of the preseason, leading the way with three goals and two assists in five contests. Behind him, other youngsters like Johnny Beecher and Mason Lohrei have thrown their hats firmly in the ring for NHL work. With a handful of practice days standing between now and the onset of Boston’s centennial season on Oct. 11 against Connor Bedard, Taylor Hall, Nick Foligno and the Chicago Blackhawks at TD Garden, here are nine things we learned from the bulk of training camp and the preseason…