By the time of the 2X releases, UC Berekely had the C30 IMP ( i.e. direct internet connection). So, once you were licensed, you got the keys to be able to FTP different 'tapes' (which included sources and binaries), be it 2X or 4X base But, since CSRG stopped focusing on 16-bit, the 2X stuff became more of labor of love and was a bit less formal and was done with cooperation with the CSRG team.
2.8BSD was supposed to be the last PDP-11 release: A final wrapup of everything, according to the release notes. 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. The formality of the release seemed to diminish a bit at each step (though that may just be my perceptions). 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...
Warner