In fact, UNIX and XPG4 Base are part of the core set of operating system related specifications, that are both in turn part of XPG4. Spec 1170 was the working name for what has now become the Single UNIX Specification. The Single UNIX Specification is a comprehensive set of operating system-related application programming interface specifications adopted by The Open Group as the single definition for UNIX systems. Novell announced the proposed transfer of the trade mark in October 1993. The transfer was finalised in Q2 '94.
Differences are in the definition of what can be branded and the conformance requirements.
UNIX 93 applies to systems which pre-date the Single UNIX Specification. This term, which is an abuse of the UNIX trademark, and should not be used, is often used in association with products that share some properties in common with systems carrying the UNIX trademark. Users of such terms should consult the trademark usage guidelines, which give numerous examples of how to correctly use the trademark, and make the necessary corrections. Conformance with the Single UNIX Specification for UNIX 95, and the Single UNIX Specification Version 2 for UNIX 98. The trade mark UNIX is licensed only by The Open Group.