Ok. Sorry for the misunderstanding.
I guess what Heiwa was referring to is that while it’s allowed to have watertight doors in commercial ships, they don’t count as escape routes. However, SOLAS allows using watertight doors even in passenger ships in way of escape routes from below bulkhead deck as long as there is at least one route independent of watertight doors. On the other hand, for cargo ships it requires to have two widely-separated escape routes (stairwell and a stairwell/trunk) from accommodation spaces below the lowest open deck, but does not make reference to watertight doors.