NORN KJOKL

Yes, of course it's not an evidence, but just an argument.
Furthermore, the loanword can be based on a non-nominative form.

Yeah, I just noticed that because the Common German intervocalic -w- often dropped without a trace in Old Norse (except it could umlaut the preceding vowel). But in this given word it did stay in several forms, and then was brought to the nominative by analogy.

"Analogy" is a little bit a functionalistic explanation.. I don't think for exemple we have a form *snevʀ for snøʀ in any form of old norse. I mean I never heared about that, but say me if that's wrong.

And thus why do we have mávʀ and not *snevʀ ? It cannot be by accident...

But we have ON snjór/snjár with gen. snjóvar/snjávar, snjóva/snjáva 'to snow' (the 'v' was often spelled as 'f'). See also sjór, sjóvar 'the sea'.

Yes, but there is no /v/ into the nominative form. That's what I mean. And so why can we have /v/ into the nominative of "gull" in some forms of norse, but not into the nominative of "snow". That's strange, don't you think ?

The presence of /v/ before a vowel is a normal phenomenon. It was dropped only before a consonant.

No, i don't think so, because analogy is rarely regular. Apart from that, these words were largely used in scaldic poetry, which also had impact on which forms had to survive.

That's what I mean. That is not regular. That's why analogy is not a good explanation. But there is certainly an explanation about why some forms are present and some are not. This explanation is surely structural. No doubt that there are reasons why we have mávʀ but not snevʀ. But which reasons ? That is the question.