Dennis Ritchie has unearthed the on-line manuals for 4th Edition UNIX,
and they are in v4mans.tar.gz. His email says:

It turns out that the source ?roff for the 3rd and 4th edition
manuals exists online here. These are versions from bowell, which
Norman Wilson will remember, and are all owned (according to the
bowell passwd file) by andrew (Hume). The Plan 9 file date marks
(inherited, probably faithfully, from bowell, and most probably
faithfully from whatever tape Andrew loaded) are in the range around
Feb 1973 for the 3rd edition, and Nov 1973 for the 4th. The dates
inside the files themselves are consistent with this.

This was clearly a feverish period. The manual pages are only a
few months apart, but besides all the system changes, the manual
was redone from nroff to troff, which appeared in the 4th and not
the 3rd. Ah, the energy of youth.