On Wed, Jan 22, 2020 at 2:42 PM Warner Losh <imp@bsdimp.com> wrote:

Berkeley's license was executed in January 74, so it might be on the list, unless there was a big delay.
That makes sense.
 
In addition to the Nov 1975 CACM paper, there's CAC 155, published by the University of Illinois on 3/15/75 which pre-dates the 6th edition by a few months. You can read it here https://www.ideals.illinois.edu/bitstream/handle/2142/32547/networkunixsyste155holm.pdf?sequence=2&isAllowed=y if you'd like. 
Thanks, that tells us it was 5th (BTW the PDF is missing page 1 in the scan - although I suspect the missing info can be gleaned from RFC 681)

BTW: There is another hint in CAC 155/RFC 681.  The line on page 2 that reads: "since the user is allowed only sixteen open files. My memory is V6 allowed more than 16, over 20 is my memory; but we would have to look at the structure to see what it is defined as.    

 

RFC 681, dated March 18th, 1975, is another instance of an edited CAC 155 report  (it seems, I've not looked at them exactly, just a quick glance) that talks about this work. It's the earliest mention of Unix in an RFC (the next one isn't until 2 years later for an email address for Dave Crocker DCrocker@Rand-Unix in RFC 724 in May 1977 after which it explodes in references).
And that pretty much syncs with my memory of the time.