It took 33 years after the founding of the seed NHA league (which became the NHL) for a team to come back from a 3-0 deficit in a seven-game series – never mind the seven-game series wasn't the standard format, that's irrelevant.
Exactly 33 years later, the New York Islanders overcame the Pittsburgh Penguins when their nose was to the grindstone.
You're astute is you've done the math and figured that that means there should have been a comeback in 2008 – 33 years on from 1975. What you're missing, just like the Canadiens marketing money grabbers, is that no season took place in 2004-05 and the NHL skipped a season of play in their own books. That means that the Canadiens (I guess St. Louis missed the memo), in their 99th season of play have put themselves in prime position to be the first team to pull off the incredible feat.
Robert L has a nice entry on the power of numbers in the Canadiens organisation as he focuses in on unlucky 13.
While I appreciate the effort, the connection of the number 13 with the Canadiens specifically is tenuous. I would suggest there's much greater cause to believe in the power of 33.
Invoking the greats (3 Montreal boys who've done the deed – albeit with a Boston team)