Very nice. It doesn't terrify my eyes at the length when I open it now ;)
A few more edits to one of your containment paragraphs.
All attempts to study SCP-XXX are to be made by D-Class researchers, specially screened for linguistic skills, polyglot status, or interest in dead languages. These researchers are exempt from monthly termination procedures. They are to study the catalog of SCP-XXX-1 objects and are granted access to facsimiles of other written samples of SCP-XXX. D-Class researchers are to make a detailed report of their findings without using any written examples of the language delivered once every week. Subjects are to be terminated before reaching the Third Stage of infection. No Foundation researcher is to directly study SCP-XXX, under penalty of termination.
There were a couple sentences that were unnecessary and a couple other minor edits. See what you think.
Also I definitely wouldn't get rid of all of your addendums just the ones that don't really add anything. Its just important in an SCP article that every paragraph adds something. I personally like the addendums you have currently, but I would be sure to keep them as an expandable section as to not scare off your readers.
The following two sentences confuse me after your edits.
The third stage results in [DATA EXPUNGED]. (See Document-XXX-C for an analysis of the memetic qualities of fourth stage SCP-XXX-2 subjects.)
It is currently unknown if SCP-XXX infection progresses beyond the third stage, due to the cognitohazzard that second and fourth stage SCP-XXX-2 subjects express.
Is there or is there not a Fourth stage? If there is how do we not know if infection can progress beyond the third stage? Hope that makes sense.
Good luck on the article and I hope this helps.