It was fairly widely known in the network engineering community in 2003/2004 that the "Echelon" system collected an extensive amount of domestic data for each of the five eyes, using legal dodges where a foreign agency (like GCHQ) would siphon american/canadian data and feed it to the NSA and CSE, and vice versa.

Those who knew how much the system had changed from satellite-intelligence gathering (from the era prior to transatlantic/transpacific submarine fiber, where most phone calls and international data were satellite based), to tapping fiber at submarine cable landing stations and "partnering" with major telcos, were totally unsurprised.

Echelon was never publicly acknowledged. Carnivore was explained as only targeted at suspected criminals under investigation. Snowden's revelations were the first hard , undeniable facts in the matter showing the true scope of the unconstitutional activity.

You're right that they never admittee it directly. Their defense was funny and an indirect admission:

https://fcw.com/articles/1999/06/02/congress-nsa-butt-heads-...

Anyway, it was all over US media from 1999-2001 plus European Parliament with plenty testimony and recommendations. And again, the link encryption recommendation was in US security requirements anyway.

Of course people knew it was going on but Snowden has put it beyond deniability and that is very very important. We now have (for example) the CEOs of the biggest tech companies in the world able to talk about this stuff. That could never have happened before Snowden.

Yes it was. Evdn mass audience heard with the reporting in Guardian, USA Today, and so on starting in late 90's. Not to mention awareness that Enemy of the State created which NSA considered one of worst events to ever happen haha.