Ok I finally read most of the thread but one thing I didn't see mentioned is that all these Twitter accounts Hirtes has usually require a mobile number for verification.
I checked a few of them and he either has access to a large number of disused phone numbers or is actively paying for a service which gets him burner lines. There are services you can pay online which will give you access to a number for a period of time, however without paying extra you will usually have all OTPs from sites like Twitter filtered because the numbers are known to be used for autism.
He probably looks like every other generic elderly-before-his-time bald fat man and thus the few times he's waddled out into the public sphere no one has noticed.
I mean I guess someone could go to his address with the specific intention of getting a picture of him, but he probably almost never leaves the confines of his concrete cube so who knows how long you'd be waiting, even if it wouldn't be wasting your time trying to get an image of what's arguably the most pointless person alive. Presumably even all the furries he's pissed off over the years have better things to do with their time than mess with him, which ultimately says a lot about how much he's worth.
Its also possible his dox are outdated, inaccurate or simply vague (implying he has an arrangement with someone else who receives his mail). Obviously 10-20 years ago receiving mail was a big deal but not so much anymore.
For instance the OP states his address is
"505 S 6th St Apt 608"
His 1998 dox claim (which matches with the address he listed on his website in the 90s)
"505 So. 6th St #226"
Its possible in the past 20 years he has moved apartment within the same complex, however its a little weird having two different addresses within the same building.
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I found this Livejournal post which as far as I can tell has never been linked or directly archived anywhere. The person claims to have known Hirtes and again makes mention of his "disability" which no one knows of.
Best explanation of Hirtes that I've found so far: disabled, lonely, and clingy.
https://fiskblack.livejournal.com/19831.html?thread=178295
http://archive.fo/SgISq