The BSD release order - 3.0 BSD is the replacement for 32V, 4.0 is the first real update and 4.1 was the so-called 'FASTVAX' stuff Joy did as part of the UNIX/VMS bake off with Stanford.  4.0 and 4.1 are very similar.   4.1 lived 'in the wild' about 3-4 years as the standard 'BSD' and any one with Vax (certainly at a university) got the BSD tape.  That is the code base that Rob Gurwitz used to write the original BBN TCP -- which did not use open (/dev/ip  /dev/tcp/hostname or /dev/udp/hostname) like MIT's ChaosNet.

4.1a was Bill's first attempt at rewriting Gurwitz's code and creating sockets.   Only a few people had it (I was one) - but it did make it to a number of the IETF beta testers -- the MIT folk I know had the tape - Noel might know whom there they had it.   4.1b replaced that about 3-6 months later but I'm not sure it left UCB very far -- I ran it on one of the CAD machines as 4.1c was being created.  IIRC B was the first to have Kirks FFS in it and we were pushing the FFS code with our cad programs that beat on the FS pretty hard.    BBN might have had 4.1b, as I think that is where Gurwitz & Walsh started the BBN2 code.   4.1c came pretty soon thereafter as the 'beta' for 4.2 and that also went to IETF folks.   Joy left for Sun, so I know Masscomp, Sun and DEC all had copies of 4.1c.   San wnj, Kirk and Sam completed the beta, and got the formal release creating the BSD 4.2 release (which as Larry points out was the first truly networked UNIX) and that went just anyone with a UCB license (and all hell broke loose because - Henry Spencer's famous '4.2 is just like Unix, only different' quote).   BBN released their alternative Network stack for sockets (a.k.a. BBN2 or Bob Walsh version) and that fight started.  About a year or so later Kirk and Sam got 4.3 out which was putting back in a number 4.1-ism so not so much code broke, I think Van Jacobson's stuff up the hill at LBL went and some of the new BBN stuff.  4.4 was at least a year after that.