2.8BSD was supposed to be the last PDP-11 release: A final wrapup of everything, according to the release notes.
Yeah, that sounds right. Bostic had moved into CSRG and I think he was hacking on it less and less. Also Ultrix/PDP-11 was out by then and Fred Cantor had sort of displaced Keith as the PDP-11/UNIX wizard.
However, there were a lot of PDP-11s in specialized niches that weren't easily replaced by more modern hardware, so 2.9, 2.10 and 2.11 happened as well.
You tell me from looking at the sources, do you know if there was any back population to these releases from DEC? The Ultrix team (aps et al) had fed CRSG drivers and some stuff for the Vax. Fred had a goal (took some pride) in trying to make the PDP-11/Ultrix release very much plug and play, but I had personally lost interest in the PDP-11 by then so I was not watching it directly, only socially knowing many of the players.
The formality of the release seemed to diminish a bit at each step (though that may just be my perceptions).
Well, the formality of anything before that was happenstance. Because CSRG was getting more formal, I think Keith and company were trying to parrot the same schemes. As I said, 4.1 and before like, Research was sort of the state of the world when Joy made the tape.
To be fair, disk space was expensive. So keeping a big hunk of space dedicated to the 'release bits' was not really reasonable much less imaginable. It was only with CRSG that for the Vax there was 'enough' hardware to have test machines and dedicated distribution.
By the time we arrive at 2.11BSD, the tapes were produced by USENIX where you had to send proof of license to get the tape... These releases were driven by Seismo, and the USGS and/or military deployments from everything I've read...
That sounds right. By the time of later 2.X versions UCB folks were much less involved and I think you might be that USENIX took over some distribution work (I was not on the board then, Steve might have been).