I was wondering if anyone that has some knowledge of the numbering system used for these documents in Bell might be able to comment on this in any way. What I've been able to make some determination on is:

700-prefixed call numbers appear to be general Western Electric stuff, most of these manuals being related to switching, power, hardware, etc. However, the UNIX 3.0 manual and 4.0 reference guide are both under this series too. I imagine this was simply because the computer systems group hadn't been formally spun off or otherwise received directive to manage UNIX documentation at this point? In any case, I'd be curious what all else may have gotten 700-series call numbers before the 300-series took over UNIX docs.

As for the 300 series, as far as I can tell 300 is the umbrella for AT&T Computer Systems, with several sub departments handling slightly different (although overlapping in circumstances) concerns. What I have managed to determine is that 301 series encompasses the original System V version documentation, a few "Level II COBOL" documents, as well as some M68000 and Z8000-specific versions of docs (I didn't know UNIX System V ever hit the Z8000, that's cool).

After System V gold, the wealth of UNIX documentation appears to come from code 307-X instead, I'm assuming 307 is whatever permutation of USG/USL happened to exist at the time. However, there are a few other codes that seem to sporadically be involved in UNIX docs as well as other computing docs:

305 - This one is hard to pin down, they've got the basic 3B2 docs, some other guidance docs for non-20 3B computers, and a mishmash of language tools like assemblers, a BASIC interpreter, compilers, and a few odd technical bulletins for products covered in other groups

308 - Documentation on a whole mess of software utilities with some odd Sys V manuals sprinkled in. You've got stuff like the "Office Telesystem", Instructional Workbench, more docs on BASIC, Pascal, and COBOL, some Fortran stuff as well, and a few other reference documents

310 - Seems to be entirely related to Documenter's and Writer's Workbenches. Whats odd is there is also a pretty even split of DWB and WWB documents in the 302 and 307 groups, so hard to say why the split, maybe a secondary department producing supplementary literature? Very low call number suffixes, so possibly 302 transitioned into 310 for DWB/WWB support

320 - Might be the "standard systems" trade books arm as opposed to the version/system specific documentation gotten from USL directly. This list contains books like the SVID, Bach's Design of the UNIX Operating System book, some programming guidance books, and the UNIX Programmer's Manual 5 volume series with the metallic alphabet blocks on the cover (echoing the V7 trade release). What's interesting is call number 320-X comes back around with SVR4 as the call code that a number of 386-specific manuals were published under.

341 - This one is very odd, a higher call number than any of the others, but the only docs I could find under this are the System V gold Document, Graphics, Programming, and Support Tools guides, which curiously weren't published under 301 like the rest of the documentation for that version.

It appears Bell also opted to have different documentation sets for different processors in SVR2. We kinda see this later on with i386 variants of the SVR3 and SVR4 documents, but I don't think we ever quite see this wide of a spread of docs straight from AT&T after this.

Also, among the many documents (one I didn't add to the list yet) is one referring specifically to UNIX Release 5.3, not System V R3 or anything like that, but a Release 5.3. I know I've seen "Release 5.2" listed in a few places, which had me curious, is there a well established record of what happened with internal (non research) UNIX after System V was branched? Whether the development stream simply became System V development, or if there was still a totally separate UNIX 5.x branch for a while that, while borrowed into System V at necessary times, did still constitute a distinct branch of development after the initial System V release. I know there is at least evidence of aspects of System V being put into CB UNIX 2.3, meaning CB 2.3 was post-System V, that would make a compelling argument for there being some more development work between CB and USG folks before they put the final bow on the UNIX/TS project and formally routed all efforts to System V.

I'm sure there are other little nuggets of information hiding in there, but that's my digest from this thus far. If anyone knows of any other such efforts to produce a listing of all known UNIX documentation call numbers from AT&T, I'll happily contribute this to their efforts.