If you find something out and you never tell anyone and no one knows about it, then you die and your discovery dies with you and no one knows about it again. Then some one else comes around and discovers the same thing and tells everyone about it. Who is really the person that discovered the thing for that society?
The steam engine was first developed as a toy in ancient greece. Does that mean that Thomas Savery did not invent the steam engine engine some 2000 years later? The difference is it took off from his invention (new to him and everyone in that society but not a new idea or item to the human race)
And now back to your topic.
Sorry. I get all "pissy" about this Leif guy.