I am unfamiliar with the history of the piece. Many things are possible. He may have "mostly wrote" it in 1992 and then "polished it" for a 1994 Oita conference, but was somewhat sloppy in internally updating everything date-dependent like the coup part. People also can be very flowery/metaphorical about using the word "coup". Not sure if they even have attendee/speaker lists online for those Oita conferences anymore, but that might also help if he wasn't at all of them. Bitrot / entropy can corrupt the digital world as well as the physical, just with more checksums if the referents still exist. ;-)
I found a source that confirms the 1992 or 1993 date: https://people.well.com/user/hlr/vcbook/vcbook7.html
“Two years later [after the first conference in 1990], I was invited back, along with John Barlow […].” “[…] which explains why I was invited to Oita in 1990, and why Barlow, Johansen, and Johnson-Lenz were invited to join me there in 1993.”
While 1992 vs. 1993 is still ambiguous (either 1993 is a typo, or the invitation was two-and-something years later), the text confirms that there was a second HyperNetwork conference in Oita in either 1992 or 1993, and that Barlow was invited to it.
EDIT: Another source: https://www.eff.org/pages/complete-acm-columns-collection
“Will Japan Jack In? For the October, 1992 Electronic Frontier column in Communications of the ACM by John Perry Barlow […] At a conference on globally networked computing in Oita Prefecture in February, I was astonished to hear a number of Japanese corporate officials […] proclaim enthusiastically the potential of the "Hypernetwork"[…].”
This would imply that there was a Hypernetwork-related conference in Oita in February 1992 that Barlow attended.
Ah. Good searching! So, maybe the 800,000 computers was "in DNS but un-pingable IP hosts" (dial-up was a big then then) or maybe included non-IP "networked" hosts or who knows.. Anyway, I agree that your finds make it more likely to be 1992/3 than 1994. Thanks!