I think you're right, the data in events.dat seems to be file names for .wav
and .mp3 files in the sounds directory (although really in sounds.dat).
Looking at descr_skeleton.txt which seems to have much of the real
data in skeletons.dat shows the _basepose.cas, a lot of the _idle .cas's,
and the weapons entries with _Primary don't have evt associations.
I guess weapons and soldiers not doing anything don't need to make sounds.