It's not entirely impossible - The difference in body shape between a male Roegadyn, Au Ra and Lalafell is preeeetty big, but armors can be refitted nevertheless. Plus, Au Ra prove that textures can be a thing as well.

I wager whenever an armor cannot be easily re-fitted by simply de-forming it, it'll provide an issue. I had lattice presets in blender for my skyrim modding which allowed me to conveniently re-fit armors modeled for one body to other bodies and I'd not be surprised if SE uses a similar procedure - model a base armor, then deform it with preset deformation patterns for the races and do some fine-tuning if things look off. Just a guess, tho.