US patent law forbids ...
"US patent law forbids the identification of earlier versions of an invention – called prior art – by third parties"
Why? That's stupid.
But then, so is MOST of US patent law. Can't allow the TRUTH to get in the way of bogus patents when it comes from third parties, can we. Oh no.
I guess USPO knows that if third parties were allowed to dispute patents, 99% of us patents would be proved invalid. That's the only reason I can think of for having such a daft, and very obviously WRONG, law.