I have read “Cod” by Mark Kurlansky and recently read an article in American Heritage about Zuane Pizzagano’s map from the early 1400’s but I have yet to see anything that claims to be from Cod fisherman drying their catches (dropped possessions, maps, written stories from the period...) or anything that truly says these assertions are something more than fancy. What else has been presented for evidence?
I've answered a very similar question before. The answer there touches on Kurlansky's claim and shows it has no evidence, and also, provides more details and further reading recommendations.
If you have more questions, feel free to ask here