I would not think the vents would matter until you would get to the top deck, by which time, the ship would have most of her critical forward compartments flooded anyway.

I guess the real thing to remember, is the ice cube tray idea.

Yes, the bulkheads are sound, but they are not topped off with a watertight top.

So, if enough damage underwater is letting in water to bring the bow down by the head, that equalibrium will be broken ( I think it was anything over 3 of the first five being damaged) and the ship will fill compartment by compartment until she can float no more.

Then, as the ship really starts to dip and her superstructure goes under, you have every orafice such as vents, windows, and staircase shafts letting water in.