His corpse was dug out less than 30 years ago. It was preserved by the ice, right? Isn't that the whole point of what you're saying?
Then, when Moria stole it, I suppose he had the means to preserve it someway.
Big relates to the physical size of Nidhoggr. You can't say that this size relates to significance while Nika is so small.
You can compensate by being a clear element, even if you are not talked about, but both?