I was just googling around and found this:
I was reading through and noticed this at the end:
I was really surprised to learn this, because a couple of days ago I was having trouble exporting a sword mesh I modeled in Blender. For some reason, the number of vertices changed on export and I had no idea why. In my case, some vertices were duplicated rather than erased. My sword model is already very efficient, even more than the swords already found in the game, but has a lot of duplicated vertices (like the swords already found in the game) to define sharp edges.
In the end, I managed to solve most of the problem by re-exporting the exact same mesh with the Blender NIF Scripts for Blender 2.49B again, but there remains a difference in the form of a duplicated vertex in the scabbard I couldn't avoid after the export. The mesh in blender and the exported sword have the exact same amount of triangles (less than 900), but the exported one always has an extra vertex. It's no big deal now, but the first time I exported it, the sword ended up having shading problems because of some vertices that got removed and others cut, even though no such geometry was present in the source .blend file and I've no idea why re-exporting the same unchanged mesh solved the issue either.
Anyway, what I'd like to know is if there's a way to disable this PyFFI functionality and leave the meshes untouched on export? I'm a noob when it comes to 3D modelling, but I'd think experience modelers would prefer to optimize their meshes themselves. I didn't even knew what PyFFI was when I installed the Blender NIF Tools, I just thought of it as just another obscure requirement, but now that I know it actually makes judgement calls for the user I'm concerned about the fact that the version required for running the NIF export tool is not the latest one released. I'd appreciate if someone out there could shed some light here. I'm not even sure if what user Arthmoor said is true, but based on my results it makes sense to me.