The internal chapter count deviates from the in-game chapter count. Within the game the Great Southern Forest belongs to the same chapter as Tien's Landing. Internally however the Great Southern Forest is part of chapter 3.
As a consequence all the filenames are slightly off. j04_arena_tavern.sav e.g. belongs to the in-game chapter 3, but the internal chapter 4 - hence the 4 in the filename.