New Sweden: the US's long-lost 'secret' colony

I guess it's a secret to the Brits and the BBC. We learned about Swedish colonies in the Delaware Valley area in fifth grade history class.

So secret that it had its own U.S. postage stamp, as shown at the top of TFA.

There's lots of things that people learned in elementary school in the UK that I don't know about. That doesn't made them a secret.