See also: Sun Microsystems' logo
It's been a while so I may not have the numbers quite right.
Anyway, there was some overlap in nomenclature, so a version bump of the SunOS naming (and Solaris numbering) implied a shift from BSD-ish to SVR4-ish, as I recall.
(And I worked for Sun for a while after that, and used Suns a ton around the shift)