Earlier quoted context omitted.
There's no proof or mention that they didn't. There never will be, ever. Yet we have to make decisions, even in the absence of evidence pro or con. Given that they don't disclose "wittingly" what they do, given their mission, and given what appears to be their interpretation of their mission as revealed by Snowden and others, we have to assume the "worst" within the realm of possibility. They did it, until they show…
Let's remove the hyperbole and call a spade a spade. So, you want them to prove a negative? Just trying to be clear.
I bet a dime-to-a-dollar that should they be accused, they'd release a non-statement to the press:
"We cannot comment on...."