No. Rather than issue a direct correction to their initial story which so falsely represented the facts on the ground that all of the US's largest internet companies simultaneously issued categorical denials, the Guardian ran another article that redefined the term "direct access", knowing (as they had to have) that their own original interpretation of the term, in black and white in Greenwald's original reporting, had been repeated as fact by numerous major media outlets.

If the tech companies have been slandered unfairly, why don't they sue the Guardian?

Because The Guardian has 19,998 more documents that they don't know the contents of.

If they have have acted properly, why should that stop them?

It's hard to lie effectively when you don't know how much of the truth is known.

Because nobody, probably not even at the NSA, is confident that they actually know the full extent of what's going on.

So true. That's one of the most dangerous aspects of conducting this type of thing in the dark.

They think the clear denial and resulting walk-backs are enough.