It's safe to assume that the vast quantities of documentation he liberated have enough newsworthy material in them to last those with access a very very long time.

Greenwald and Poitras have said this publicly many times. They have years worth of material to report from the cache of files.

Perhaps more charitably, it will take them a very long time to parse it. It's too bad that they can't responsibly crowdsource the work.

It's also likely or possible that other disclosures are labeled under Snowden in order not to compromise or reveal the existence of a new source.

In fact, Bruce Schneier believes there's another, unknown NSA leaker besides Snowden: https://www.schneier.com/blog/archives/2014/08/the_us_intell...

It was already confirmed in the documentary CITIZENFOUR

That's the third leaker, not the second one.

1. Snowden

2. Unknown NSA leaker

3. Unknown National Counterterrorism Center (NCTC) leaker

This is all part of the initial haul. They're checking all the documents one by one to make sure they don't reveal information that would make intelligence agents and others at risk. They've partnered with quite a few media organizations to spread the workload. Amusingly enough, you could say that Greenwald et al. are doing the OpSec the NSA should have been doing in the first place. :)