My default assumption is multiple agencies have made a preliminary identification of every single poster on this forum and actively track all content. They don't share their information with the others very well and there are overlapping projects of which the various parties are unaware.
There are overlapping agents provocateurs as well. Perhaps they are busy writing reports on each other.
And this forum is only one of many that gets surveillance. I expect that even our opponents contributing to the DU website get similar efforts directed towards their postings.
My guess is that these projects are not viewed as prestige assignments to the agencies involved, and get sloughed off to contractors, who charge absolute top dollar rates.
Good money for the companies that get the projects. It really pays to know the right people.
Quality control would not be a particularly strong element and perhaps 25% of the poster identifications would be incorrect. Not that it would matter all that much. Nobody would ever use those names, would they?
This is all just speculation for your entertainment of course.