http://www.levenez.com/lang/ says 1978 for oawk and
1985 for nawk.
regarding
http://www.levenez.com/unix/, 1978 is between v6 and v7,
and 1985 is between SVr2 and SVr3.0.
The preface of "The AWK Programming Language" says: "Awk was originally
designed and implemented by the authors in 1977, ... so awk was enhanced
in a new version made available in 1985". About the book and the
enhancements the preface says that "The examples in Chapter 1 use only
the facilities of the new version; many examples in later chapters take advantage
of new features. This version of awk is part of Unix System V Release 3.1.
Source code for this version is also available through AT*T's Unix System
Toolchest software distribution; call 1-201-522-6900 and log in as guest."
There is also info how to get it in other parts of the world.
jaap