I posted the NpcSkill.sdata file for reference only !
You are right to highlight the fact that tailored files are very common, and thus your working files shall quite never be replaced by a nexon file.
Also, the newly listed skills can use some "new combinations of old effects" or truly new effects.
What I designate by "effect" is the "TypeDetail" field of the skill, this field defines a lot of parameters of the skill, nexon had added some new types (and will follow). The new skills that use new effect(s) (TypeDetail(s) unknown of our server) can of course not be used as they are.
2nd source of uncertainty, the mobs skills are in turn referenced in the Mobs definition as the Attack Type fields (column "Type" in monster editor of shStudio), this field is only present in dbo.mobs table (not in monster.sdata) so we have no evidence that skills defined in NpcSkill.sdata are used are used by some of the mobs and when they are, we don't know with which parameters.
last point, the file was updated by nexon since I posted it, here is the version 228 (3 new skills (and 4 rfu)).