Somewhere between UNIX Release 3.0 and Release 4.1, a portion of the User's Manual was split off into a separate Administrator's Manual, leading to a reordering of the sections among other things.  In the directories, these pieces would be placed in u_man and a_man respectively. There may be some evidence of the manual being intact as of 4.0 or at least not completely separated. I've found consistently that references to manpages in the Documents for UNIX Release 4.0 collection follow their pre-split numbering and all refer to the User's Manual. The catch is that all references are to the UNIX User's Manual Release 3.0, so this may not point conclusively to the state of /usr/man on disk at the time. The Release 4.1 Administrator's Manual hasn't turned up yet but the User's Manual reflects the renumbering and is less the a_man pages. To complete the circle, the various Release 5.0 revisions of the documents do refer to the Administrator's Manual where appropriate. Was the manual getting split up of any great shock or was it to be expected as the software grew? It would come to happen again between SysV and SVR2 with p_man. Out of curiosity I checked how my own manpage set is organized, it seems to be of the research order, with special files in section 4 rather than section 7 for instance. I've never studied how far reaching the different orders are. - Matt G.