StatsThroughSkills III and StatsThroughSkills IV mods downloaded through CDDA launcher have exactly same formulas. There is only slight diifference in the lua code - version IV uses efftype_id type and will probably work in more recent experimental versions of CDDA. Bonus stats are applied through effects and are recalculated once a day using on_day_passed callback.
StatsThroughSkillsmod shipped with experimental CDDA have different formulas. Bonus stats are added directly to base stats and recalculated once a day using on_day_passedcallback, on new game start using on_new_player_created callback and after any skill is increased using on_skill_increased callback. There is also migration code from some older original version of the same mod. This version supports having any initial stats (either 8 8 8 8 or other combinations).