Hello, let me answer to you. Katkat's really great artist and done/do new models. If you open any of them (for ex., using Nifskope) you can see path to used textures (marked by flower) - and often this path is to this @ folder - so it's used not game's changed resource but this new one.
The idea as I understand is to not overwrite too mush but only needed peaces. Also in some thread she explained that sometimes textures are used not for the objects for which they were created (and if my memory is good, she point the situation where for lantern the texture of city wall is used - which is toooo huge for such little peace.
Anyway, you shouldn\t worry about this situation, all new stuff is added to game exactly so.