As I know, few watertight rooms existed at the bow. Some of the rooms should be un-flooded before the breakup because the flooding water line is always lower than waterline outside Titanic. Furthermore, the dryness of rooms before breakup was more likely a transient phenomena, when water was still finding their ways downwards (into another watertight compartment). The speed of water flowing downward may lag behind the speed of the sinking speed.
When the breakup occurred, it was expected that some rapid and chaotic flooding from the breaking point happened at the rear part of bow section, but the rapidness / chaos should be less severe than that of stern session submerged after 2.20.