NMM? That might explain it then... NMM is quite broken, that's why the Nexus abandoned it and started making Vortex instead.
Well, if you ever feel like trying to fix this again. One last thing you can try is to go into your FNV Data folder and see if you have a Meshes folder, if you do, see if you have a armor folder, if you do, see if you have any folders with "powerarmor" in the name. If you do, try deleting those.
If you still have any problems with the armors, you can then try to do the same with a textures folder instead of the armor folder.
Examples:
*Your FNV folder*\Data\meshes\armor\*folder(s) with powerarmor in the name*
*Your FNV folder*\Data\textures\armor\*folder(s) with powerarmor in the name*