There's evidence[0] of other, possibly currently active, whistleblowers leaking documents from inside NSA. This database includes those leaked documents as well, as it mentions XKEYSCORE, which Snowden has said he did not leak.

[0]https://www.schneier.com/blog/archives/2014/08/the_us_intell...

He had access to the NSA servers even after he fled using credentials from other employees. Sorry I can't find a citation but I read about it about 6 months after the initial leak.