Nick asked for an exmple of AT&T code in Gnu.
Warner explained a spectrum of ways and degrees of innocence
by which that might happen.
The example I have in mind is "calendar" from v7, whose very
idiosyncratic implementation appeared in Gnu with only
cosmetic changes. It has been modified since by discarding
archaic efficiency hacks, but still uses the same quirky
basic method.
Conceivably Gnu's implementation was done only after v7
code was made public. But in any event, it has been
distributed without attribution.
Doug