System 9 was really just about some compatibility layers in preparation for OSX, as I remember it.
(And, yes, 7.6 was a major step in terms of stability. There was also some pre-PPC, pre-OpenDoc version of System 7 that was pretty stable, but with all those major integrations that came with the further iterations, things became a bit "delicate".)
IIRC Mac OS 9.0.x had significant changes for users directly booted into it, as did 9.1 (though to a lesser extent). I think it was 9.2.X that was mostly focused on usage with Classic.
Then 8 felt like a huge shift to the modern. Yes, would have been weird to be 7.7. An ideal break point.
Seems odd the clones licensed by OS version, not duration.
9 didn’t have the same change feel.