System IV was never released

A brief history of UNIX

http://www.info-discovery.com/solaris/html/node4.html

>I had heard (in the late 80's), that ATT System IV had become public domain. Did that happen?
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>>>http://www.eweek.com/article2/0,4149,1400161,00.asp
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>>A tangled web ....
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>>In the late 1970's Microsoft licensed UNIX source code from AT&T which at the time was not licensing the name UNIX. Therefore Microsoft created the name Xenix. Microsoft did not sell Xenix to end-users but instead licensed the software to software OEMs such as Intel, Tandy, Altos and SCO who then provided a finished version of their own Xenix to the end-users or other customers.
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>>SCO introduced its first version of Xenix named SCO Xenix System V for the Intel 8086 and 8088 in 1983. Today SCO Xenix is one of the more commonly used and found versions of Xenix.
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>>I think there is even a version of Xenix somewhere on one of my old MSDN subscription disks. Or was it REXX ... ?