With Joliette's win in game 7 last night over Saint Eustache they became the first junior team this year to complete a series win, despite losing the first three games. Usually happens 2-4 times a year.
La Peche did it to St. Isidore in the EOJCHL in their league quarter-final, I don't know of any others at the moment... so Joliette is probably the first Tier II team to do it this year.