The AT&T lawsuits are a moot point, as they were all settled in the early 1990s. They are the sole reason why FreeBSD and NetBSD even came into existence – by forking the 4.4BSD-Lite codebase after the disputed code had been eliminated or replaced with non-encumbered reimplementations. Otherwise, we would all be running on descendants of 4.4BSD-Lite today.
The lawsuit was settled in Feb 1994, FreeBSD was started in 1993. FreeBSD was started because development on 386BSD was too slow. It took FreeBSD until Nov 1994 until it rebased on BSD-Lite 4.4 (in FreeBSD 2.0.0).
At the time 386BSD and then FreeBSD were much more mature than Linux, but it took from 1992 until the end of 1994 for the legal clarity around 386BSD/FreeBSD to clear up. So Linux had about three years to try to catch up.
The lawsuit was settled in Feb 1994, FreeBSD was started in 1993. FreeBSD was started because development on 386BSD was too slow. It took FreeBSD until Nov 1994 until it rebased on BSD-Lite 4.4 (in FreeBSD 2.0.0).
At the time 386BSD and then FreeBSD were much more mature than Linux, but it took from 1992 until the end of 1994 for the legal clarity around 386BSD/FreeBSD to clear up. So Linux had about three years to try to catch up.