Indeed like Olaf said, ...allow me to place a reply, even if I am learning Swedish, not Norvegian.
It's the genitive by definition, right? to describe situations of "ownership" (not strict possession) and including "figurative ownership". Thus situations like "...X of Y", "...X from Y", "... X by Y" ... Which turns into "...Y+s X"
Like in
- the inhabitants OF the country
- the fifth OF/BY Beethoven
- A research OF(lasting, which took) many years
- the book FROM Paul
Now the question is on this one with 2x OF ... "the result OF (many years OF) research".
Which of the 2 OF's applies for the genitive? Not sure if there is a grammatical trick to find that out,
but of course it's "the result OF (whatever) research".
Hence a Swede would (probably) say
- "(många år av) forskning+s+resultatet"
(and Swedes would probably prefer to write the latter as one long compound word)