@allison @ezio Specifically, they named the new product Solaris 2.x, with the underlying operating system named SunOS 5.x. The BSD-based SunOS versions were retroactively renamed Solaris 1.x, with the underlying OS called SunOS 4.x.
This is indeed very complicated, and most people just kept calling the old system SunOS and the SysV-based one Solaris.
Source: I was working for Sun around the time when Solaris 2 because usable.