i just looked into the map files, every cpk in it is the collection of files for a location (dungeon, town, area...) or a game feature (like Turtlez transport and system files).
For example, lanR is the file for Lhant, there are all the voices, story texts, models and textures that will be used in the town. Zhonecage works the same way, its file is zoneR. Lando said that the JP cpks should be repacked with US scs folder, this should fix the black bar/missing texture error too.
donkatsu: try it, if you get a different sized file then there was a problem last time