Wow, this is a new take, first time seeing the bulk of the information in addendums.
Containment Protocol:
Pending.
Surely they would monitor ISPs and other internet traffic for any signs of the anomaly, right? Provide at least a small containment protocol for the time being.
Description:
The existence of this entity has been a topic of debate within the Authority.
Just a preference, but replace 'a topic of debate' -> 'contested.'
Alleged Discovery:
On September 2009 Echo-51 operatives
Add a comma in-between '2009' and 'Echo-51.'
Echo-51 evaluated almost a dozen different proposals before settling for Dr. ███████'s
Replace 'almost a dozen' with 'approximately twelve.'
Dr. ███████'
Personal preference, but I think it would be better to just list off a random doctor's name, helps the reader connect more with the individual in question.
Development advanced smoothly over the two years that followed
Condense to: "Development advanced gradually for two years"
who began to crawl social media looking for posts that matched RPC-███'s writing style and sentence structure.
Replace 'crawl' -> 'monitor' and 'looking for' -> 'searching.'
Even though no posts appeared the fit the profile, the analysis yielded staggering results, indicating that over 40% of publications on popular social media site ████████.com had been written by the same person.
Replace 'Even though no posts appeared to fit the profile' -> 'Although no posts matched the profile.'
Also, replace 'staggering' -> 'several.'
In every case the program
'In every case' -> 'In each case' and add a comma following 'case.'
RPC-███ was found by chance
Might be preferential, but 'found' -> 'discovered.' Comes off as more clinical.
Now, one thing I wanted to note that as I read this, this began slowly feeling more and more like a cognitohazard rather than an anomalous internet user as I've been going about. I'm not sure whether this is intended, but I like the narrative aspect that the article gives in the addendum, seeing as how it's the meat and potatoes of the piece.
Is it possible to give the reader the context of how RPC-399 types? Perhaps in the description or elsewhere? It may give additional imagery to the reader, as well as the content pertaining to their posts. I believe this would help the article greatly as well.
For now, focus on the elements that I've mentioned and see if you want to add anything else. Add a picture, too?