I was just wondering, what in the poetic edda is from Iceland and what is from Scandinavia? What I mean is: did Snorre or anyone else add to the mythos or did they only write down verbal legends from Scandinavia?
Hello anon and thank you for the question.
The short answer is that no one knows for sure and there is no conclusive evidence regarding where individual parts were composed for the Poetic Edda. It is written by multiple anonymous sources from oral traditions passed down by word of mouth. Anything composed before 870 is assumed to be most likely to have come from Scandinavia, while most young poems are likely Icelandic (at least in terms of authorship, if not content).
However, Snorri was author (or at the least compiler) of Prose Edda (NOT Poetic Edda) in around 1220 in Iceland. What he added into the content is for anyone to guess and many believe that parts were heavily influenced by Christianity (which had been the religion for hundreds of years by that point in time).
So the only thing we know for sure is that we do not know for sure.