So what? The Vikings didn't do anything with their "discovery". It was basically a secret. Columbus deserves credit for discovering the Americas. He didn't find what he was looking for, but he found a lot more. And everybody knew it and headed west right after him.
“The Vikings didn’t do anything with their “discovery”. It was basically a secret.”
Secret fisheries perhaps.
It might also be dependent on the health or longevity of a culture at the time of discovery.
That’s like saying the Germans discovered pi when in actuality pi was discovered 300 years earlier in India.
Discovery is discovery and when people unknowingly take credit for it is still discovery but only in the context of cultures that assumes sole proprietorship.